WhitakerAudio
 
New Project – Gates Executive Audio Console Restoration
Gates Executive Console on the bench

Gates Executive Audio Console in the shop, May 2017. The new power supply can be seen on the far right.

Introduction

This restoration project began in October 2016 when my brother, who runs a recording studio in Sacramento, CA, suggested it would be fun to set up a 1970s-era radio station control room for special projects and, well, just because we could. His studio has all the cool new stuff you would expect in a modern recording facility, but since we both worked in radio back in the day (he in front of the mic and me behind it), we both have more than a little nostalgia for the younger days of radio (when, coincidentally, we were both younger).

So began the search for a classic radio audio console. At the risk of generalization, there are about four basic classes of audio consoles used for radio broadcast applications, and they can be roughly divided by the era in which they were made:
• Pre-1960: tube-type mixers of limited capabilities and modest performance.
• 1960 to 1980: transistorized mixers with considerable flexibility and good performance.
• 1980 to 2000: mixers built using integrated circuits and discrete semiconductors offering considerable flexibility and high performance. This class of mixers ushered-in the era of the mixing desk—the mostly flat console with long-throw linear faders. Ubiquitous.
• 2000 to present: computer-assisted or computer-based mixing systems where the work surface is essentially an input device to the computer.

We focused on the 70s style, since it represents, arguably, the golden age of radio—a time when radio was at its peak in terms of influence (before the CD, Walkman, iPod, satellite radio, and web streaming). Having arrived at the style we wanted, the search began for the centerpiece of the project. Because of the size and weight of these audio consoles, shipping is problematic. Therefore, the eBay selection was immediately narrowed to "local pickup." After about a year of casually looking, we found a very good candidate for sale at a reasonable price. It was about a 4 hour drive from home to pick it up, but it was worth it.

The board we decided on was the Gates Executive Stereo Audio Console, manufactured by the Gates Radio Company of Quincy, IL. A trade magazine ad for this line of consoles is shown on the right. The Executive was produced from the early 1960s into the 1970s. It was the top of the line product, offering a wide list of features and switching capabilities for the then-emerging field of stereo FM broadcasting

Like most audio consoles of the day, various inputs could be switched into the separate mixing channels and routed to cue, program, and audition circuits. Each served a specific purposes at a radio station.

The Executive did all this and whole a lot more. It was intended to serve as a central mixing and control point for a suite of studios that included the control room and two announce booths. A full compliment of resources were provided for the announce rooms, including microphone inputs, cue and intercom, monitoring, speaker muting, and "on-air" light control.

With 10 mixing channels, the board was about as large as practical, measuring a full 54-inches across. The series also introduced a very stylish knob, unique to Gates, that is about as ergonomically perfect as possible. The Executive was one of the largest radio consoles made by the company during the rotary pot era. The 1971 list price in Gates catalog #99 was $5,300—making it the most expensive radio console in the book. The next largest board was the Dualux II, another 10 channel mixer, also intended for combined AM/FM stereo operation.

Radio consoles during the 1970s had a dubious flirtation with push-button switches. Examples can be seen in the two smaller consoles in the ad. Push-buttons offered a space-efficient option to the more conventional rotary switches, or the more stylish (and more expensive) lever switches (as used in the Executive console). Early mechanical push-button arrays, however, often suffered from poor reliability, and interlocking switches (where, when one button is pressed, another is automatically released) were mechanically noisy when engaged. This was not the best situation for a live broadcast environment. So, in the search for an audio console, push-button switches were a non-starter.

A well-built lever switch has remarkable reliability. And they can be operated easily and quietly in a live radio environment.

So, we were happy to find the ideal console for this project—the Gates Executive Stereo Audio Console..

In the log entries below, we chronicle the process from "sold as-is, local pickup only" to being back on the air.

Gates Radio ad for audio console

 


Day 1

I have taken a close look at the board. Generally speaking, it is in good shape. However, there are four unexpected finds:

1) The power transformers are missing. They are mounted external to the board on a small chassis. These are easy to replace. And not very expensive. This is an easy fix.

2) The monitor amplifiers are missing. The photo showing the inside of the chassis is where the monitor amplifiers should be. The monitor amplifiers are used to drive the studio speakers, right and left. I have seen them for sale on eBay from time to time. The most recent posting had one for about $75. I will keep my eyes open for these.

Strictly speaking, the monitor amplifiers are not needed for operation. If powered speakers are used, the monitor amplifiers would simply be shut off. Alternately, I could build two replacement monitor amplifiers using the original Gates diagrams. So, this is fixable, but it might take some time. I think that for the sake of completeness, the monitor amplifiers should be in the finished board.

3) The edge of the cabinet trim piece is chipped. I knew that from the eBay listing, but upon closer examination it is a little more substantial than it seemed to be from the eBay photos. I’m not sure how I will fix it. There are some possibilities, but it will require a little creativity. I’m working on that.

4) Unfortunately, somebody decided to “improve” the board at some point. The photo of the front panel shows two issues. The first is that the Master Gain controls have been removed (see the top portion of the front panel). This is easily fixed, but matching the knobs will be a challenge. The larger issue is the three holes between the mixer pots 8, 9, and 10. These are just holes. Nothing in them.

There are two options here. The first (and best option) would be to have the lower panel of the mixer remade. I could do that, at some expense. If I did the lower panel, I would probably want to do the upper panel as well so they both match. Now we’re talking about some serious work (and expense). The second option would be to install small push-buttons and wire them out as “remote control” buttons. The explanation would be they are connected to cart machine “start” functions, etc. In fact, that may be what was originally there. If you look at the knobs and imagine potting up #8, your thumb is in a perfect position to press “start”.

My plan is to focus first on the cabinet. The front panel will be the last thing I work on, since it is potentially the most time-consuming and expensive. Before I can work on the cabinet, I need to carve out a large working space, since when the cabinet is disassembled, I will need to spread out the inside wiring and hardware and leave it there until I get the cabinet back from the shop.

In the meantime, I will keep looking for spare parts on eBay that might come in handy. For example, it could be helpful to find a couple of extra "mixer" (big) knobs, just in case one breaks at some point.

Anyway, I am encouraged about this project. My estimate for completion is about 6 months. Right now, the biggest challenge is finding a space large enough to work on it.

This will be a beauty when it is done!

Interior chassis view
Cabinet trim chip
Front panel view showing missing knobs and extra holes

Day 2

Today I began the restoration project. It’s great to get started. However, I have uncovered some very troubling items. Not show-stoppers, but they will add considerably to the task.

This board has been in service at a couple of stations, maybe more. The last installation job, regrettably, left much to be desired. It was far below what one would expect for a piece of mission-critical equipment, such as this board. I must add here that I appreciate the need for speed in some situations. And, I do not like to criticize someone else's work. But, this is quite a mess.

Keep in mind that this board was intended to be used as the primary means for delivering on-air program material. As such, it is very important to have a quality installation job. Two of the most important characteristics of a quality installation are reliability and maintainability. Whoever last installed this board fell short on those objectives.

At the risk of over-thinking the installation work, it appears this board has been installed and removed from service at least two times. Fortunately, the mess is fixable.

The maintenance performed on this board is equally troubling. And, unfortunately, it is more difficult to fix. Notice the burnt resistors on the circuit board (this is one of the program line amplifiers), and the wiring of the power supply module. The extent of the mess in the power supply is hard to visualize from the photo. Among the notable shortcomings are at least two filter capacitors that were improperly soldered, with leads just dangling on the board. Missing components add to the issues.

And then there are the component failures. The white items in the bottom image of this log entry are resistors burned in two.

So, we have a challenge here.

It appears certain that I will need to repair or possibly re-manufacture the following circuit boards:
• Power supply
• Program line amplifier
• Cue amplifier
• Mic preamp(s)

Actually, that’s all of the boards.

This is doable, and the mixer will be first-rate when finished. However, it will take considerable time.

When I remanufacture a board, there is a large amount of documentation that goes with it. So, we are talking about a month or two for each board. The major steps include design, assembly, testing, and documentation. I’m fine with doing this, and it will be a fun project. However, it blows the 6-month time-line out of the water.

So, that’s the bad news. The good news is that none of these are show-stoppers. Aside from examining all of the active circuits today, I began the process of cleaning-up the internal wiring.

In this unit, there are sections of wiring that were wrapped in black plastic (electrician’s) tape. This was done to insulate the cables from open contacts. Over the years (decades) the plastic tape deteriorated. So, I pulled all of the old tape off and removed the residue. It looks much better already.

Nowadays, there are more elegant means of insulating cable bundles, which I will use when I rebuild the chassis. A heat-resistant insulator such as Kapton film will work nicely, or the more simple solution of split loom tubing.

Tomorrow I will remove all traces of the disappointing installation job done by somebody who should have known better. That’s an unpleasant task, but all evidence of the old problems will be gone.

Next weekend I plan on removing all hardware from the rear portion of the chassis (everything except the front panel). I will then have the cabinet sand-blasted and refinished in a satin black textured powder-coat. The vendor will require a week or more to complete this work, and since I am out of town for that week, the timing will be good.

I found a label inside the board indicating an installation date—1972. That sounds about right. That would make this “baby” 44 years old.

I will keep looking for another similar board, or parts from a similar board, as that could help address some of the problems identified above.

Given the shape of the board, I might have paid a little more than it was worth…but probably not enough to reconsider the decision. And, in any event, I bought the console "as is." Fair enough.

It will be beautiful, but it will take time.

Original installation wiring
Line amplifier component failure
View of power supply
Resistor failure

Day 3

Today I worked on cleaning up the external connections to the board made by somebody long, long ago.

The good news is that the terminal blocks clean up very nicely and look nearly new when done. See the before and after photos on the right.

The cleanup process was time-consuming but simple. First, the wire on the terminal was removed. Next, the excess solder was removed by using solder wick (American Beauty annealed copper, 0.130 inch). Cleaning all of the terminal posts on the board required 20 feet of solder wick. There was a large amount of solder present on nearly all terminals—far more than required. In addition, after removing the wire and excess solder, the remains of another wire were found, indicating that the original installation wires were not unsoldered, but instead just cut off. Not the best approach.

After the remains of the old wiring and the excess solder were removed, I removed the mounting screws for each terminal block so I could position it on one side. Then, after surrounding the block with absorbent paper towels, I applied a generous amount of flux remover (MG Chemicals 413B-425G). This is a spray-on product and it does a very good job of cleaning solder flux from electronic parts. In this case, because of the amount of solder residue, it was necessary to apply several coats.

When using flux remover, it is important to contain the spray and the runoff, since the chemicals in the remover may also remove paint and silk-screened lettering. A thick padding of absorbent paper towels will usually suffice. In this particular case, damaging the cabinet finish was not a major concern, since the entire cabinet was going to be sandblasted and refinished anyway.

The flux remover made it possible to get the terminal blocks in like-new condition, rather than just clean.

Be certain to provide adequate ventilation when using flux remover and to properly dispose of the soiled paper towels.

I have made an inventory of all the hardware (screws, washers, nuts, etc.) used on the chassis. I plan on tossing all of the old hardware and replacing it with new, stainless steel hardware. The cost is minimal, but the difference in appearance is significant.

I have disconnected all of the components from the chassis, as shown in the photo on the right. The next step is to remove the chassis and get it to the vendor to be refinished. But, before I can do that, I need to construct a large work platform so I can spread the pieces out in preparation for reassembly. That will involve two sawhorses and a big piece of plywood.

Looking again at the broken end trim piece, because of the way it is built, I do not see a practical way to repair the chipped section. Instead, my plan is to smooth off the rough edge and have it refinished. I can use it until a replacement can be found. As I mentioned previously, I am hoping to find a similar board that I can cannibalize for spare parts.

In parallel with the electrical work on the console, I have begun to create a new user/service manual. I have the original Gates documentation, but it is in poor physical shape. I plan to expand upon the original material where appropriate. For example, I will document to the extent possible the internal wiring codes (e.g., wire #123 goes to terminal block 1, pin 6). With the components removed from the cabinet, access to the wiring is about as easy as it will get. Part of the expanded documentation will be the configuration of jumpers on the terminal blocks. With the blocks completely clean, the jumpers will need to be reinstalled.

The documentation work will stretch from now until the end of the restoration project—possibly beyond.

Terminal block before...
Terminal block after...
Cabinet components ready for removal

Day 4

Today was a big day for the console refurbishment project. I created a large work space that allows me to spread out all of the inside hardware and remove the chassis for refinishing.

With the chassis completely removed, I will take it to the refinishing shop for a textured power-coat finish. As seen in the photos above, the original chassis is gray. I plan to change it to black. That way, the entire cabinet will be black. I think that’s a better look, and it is less expensive than doing a two color powder coat finish.

With the hardware removed from the chassis, I will be able to do cleanup on the internal components more efficiently. While removing the chassis is a bit of an extreme step, it will afford a rare opportunity to closely examine all of the internal components and to clean elements that would otherwise be inaccessible. I plan to make the most of this opportunity.

My plan is to focus on the chassis and associated electronics. I will leave the circuit boards to last, since that’s where most of the time and money will come into play (other than the front panel considerations, as described previously). When I get the chassis back from the shop, I will begin reassembling the console.

Console with cabinet removed

Day 5

Today marked a turning point for the project: maximum disassembly. At this point, the board is as disassembled as it is going to get. From this point forward, it starts getting put back together.

Having the internal hardware removed from the cabinet provides a good opportunity to examine and work on parts of the console that otherwise are difficult to access. And, even for those parts that are accessible in the chassis, it is necessary to lean into the unit to perform the work. This is an uncomfortable working arrangement, at best. Also, while working in cramped quarters, it is possible to accidentally damage one component while working on another. There is evidence of such "collateral damage" from previous installations and repairs. This is largely unavoidable in a densely packaged system such as this console.

The last point deserves some additional comment. One important consideration in any refurbishment project is what to fix and what to leave alone. Every engineer knows that judgment calls must be made for this type of work, which are not always clear. For example, while it might be desirable to replace old electrolytic capacitors on a circuit board, the collateral damage to the board itself often outweighs the benefits. Defective components must be replaced, of course, but preventive replacements may damage the board or other components. Judgment calls based on past experience guide us in these cases. For a situation such as I now have, with the console clearly out of service, with no deadline for finishing the project, and with exceptional access to all components, this is the time to make any repairs that might otherwise be considered "optional." This certainly applies to all hardware in the console. For the circuit boards, however, I plan to be less aggressive about component replacement because of concern about damaging the boards in the process.

It is worth noting that circuit boards manufactured in the 1960s and 70s are far more fragile than modern boards. Differences include the materials used to construct the boards and the traces. The greatest maintenance challenge for old boards is to avoid lifting the component pads. Modern boards have plated-through holes, which are usually quite rugged. Older boards, typically one-sided, can be easily damaged by heat and mechanical stress.

The project will take a pause for the next week or so while the cabinet is refinished. After that, the console will begin to take shape.

Console completely disassembled

Day 6

Good progress today on repairing the relay panel that had been damaged sometime in the past. The relay panel is used to mute the monitor speakers when a microphone channel is switched to Program, Audition, or Cue. There are three sets of monitor speakers—Control Room, Announce Studios, and Lobby. In addition, the relay panel has the ability to activate “on air” lights in any of three locations.

You may recall this circuit had some serious problems—two resistors burned in half and four others damaged (as shown in a photo above). All that has been repaired, and the relay panel now looks quite good. When the resistors failed, the heat damaged a couple of wires in the vicinity of the relay. Those wires were also repaired.

Other work today involved cleaning and repairing cabling. Overall, the cabling on the console is in good shape. There are, however, some exceptions—notably the wiring that used to connect the monitor amplifiers. That has now been cleaned up.

Also, I did some work on the microphone preamps and the cue amplifier. As mentioned previously, I plan on eventually re-manufacturing these boards. They are, however, in good enough condition (after some work) to be used, at least initially.

The boards can be re-manufactured at a later date and simply swapped out. That will significantly shorten the time required to get the console to work again.

Board begins reassembly

Day 7

Good progress on reassembling the major components. The card cage was put back together, and connectors attached to the line amplifier modules. The mic preamps can be seen in the photo (the four cards near the bottom). The card at the far end of the card cage is the cue amplifier. The three line amplifiers can be seen, with their covers removed. The covers will be refinished before being installed.

At this point, all wiring has been cleaned up and repaired as needed. All modules and circuit boards, with the exception of the power supply module, have been repaired as needed and cleaned.

Returning to the relay panel repairs detailed above. The reason the resistors failed is a bit of a mystery. The resistors, 47 ohm 2 W, are switched across the monitor amplifier outputs when one of three speaker sets is muted. The resistors are only taking a load when a microphone is on. The rated output of the monitor amplifier is 8 W across 8 ohms. And that assumes a full power sinewave, which is certainly not representative of human speech. And, it is intermittent duty.

The other surprise is that this must have happened over time. The resistors that burned in two certainly announced their failure with the very distinctive smell of over-heated carbon resistors. The four other resistors that were heat-damaged most likely happened over time as well. Perhaps the failure of the load resistors and the fact that the monitor amplifiers are missing are connected. Or, the 2 W resistors were simply under-specified by the manufacturer. When replacement monitor amplifiers are found (or built), this relationship between the amplifiers and the relay panel will be further investigated.

Board reassembly

Day 8

Today was the first serious work on the power supply.

The power supply module provides two outputs for use by various circuits in the console. One is 37 V dc unregulated and the other is 30 V dc regulated. The input to the power supply is a 28 V ac transformer that is mounted externally to the console.

Of all the problem areas of the console, the power supply was the greatest concern. It would clearly not operate as found, since two transistors were missing, two zener diodes were missing, and three filter capacitors were either poorly connected on one end, or not connected at all.

There is no easy fix for the power supply. The first step was to completely disassemble the unit. Once that was done, the exact condition of the circuit board and related hardware could be determined.

I do not want to dwell on the poor maintenance this unit received over the years. However, given that the failure of the power supply would take the console out of commission, it is hard to believe that the supply did not receive better care over its operating lifetime.

Moving forward, some parts have been replaced and the missing items have been ordered. Fortunately, the missing components are rather common.

The wiring needed considerable attention. The photos show the "before" and "after" pictures.

There was a considerable amount of excess solder on the board, and lots of solder flux. The extra solder was removed with solder braid, and the board thoroughly cleaned with flux remover.

After the cables were organized again (the lacing had come apart over the years), the board began to look like there was hope.

With the components removed, the power supply cabinet will be sandblasted and repainted.

I hope to be able to restore this unit to operating condition. It is possible that building a new power supply will be easier than fixing this one. The supply requirements are modest, and easily achieved today with an integrated circuit regulator. Still, the goal is to return the console to new condition, so I will try and make the original supply work.

I have noted previously on this blog that some transistors are missing from various circuit boards. Curiously, many of the transistors are socket-mounted. So, it is quite possible that they simply fell out during transportation at one point or another. I had forgotten, but many circuit boards in the early days of transistorized designs used sockets for the transistors. The assumption was that the devices might need to be replaced from time to time. As it turned out, the sockets were usually less reliable than the transistors. The practice of using sockets for discreet devices has essentially disappeared; likewise for integrated circuits (except for large processors, gate arrays, and the like).

Power supply before repair
Power supply board under repair

Day 9

Today reassembly began. The cabinet work has been completed, and it looks great. The powder-coat finish is perfect. I prefer the all-black finish, rather than the combination black and gray finish of the original.

Reassembly was more of a task than I had expected. Getting the major components out of the cabinet was considerably easier (and faster) than getting them back in. There were two major challenges. First, moving the large sub-assemblies (card cage, relay panel, cue amplifier transformer panel, program amplifier trays, and terminal blocks) back into the cabinet without scratching the finish of either the cabinet or the sub-assemblies. Second, reattaching the front panel to the cabinet.

Reattaching the front panel would be a very difficult (perhaps impossible) step for a single person to accomplish. Fortunately, after Thanksgiving dinner I had two (mostly) willing assistants (daughters) who stepped-in to save the day.

The front panel is held in place by four hinges. Reattaching them was a challenge, given the weight of the front panel and the overall cabinet itself. Once the panel was in place, I (we) attached the bottom trim piece. This was a bit tricky. When installed to precisely line up with the end trim pieces, the front panel would scrape ever so slightly along a portion of the trim. So, a compromise was made to forgo precise lineup with the end piece in exchange for no contact between the front panel and the bottom trim piece.

The scraping situation may have actually existed for a very long time. The wear pattern of the original paint on the lower trim suggested a problem that had occurred over many years. In any event, no one will notice the slight discontinuity between the end trim piece and the bottom panel trim piece. (Except for me, of course.)

There is a top cover panel for the cabinet. That was refinished in the same black satin texture powder coat as the cabinet itself. I will install the top cover only after all (or nearly all) work has been completed within the chassis. This will afford maximum accessibility to the internal components.

With the benefit of hindsight, the decision to completely remove the cabinet was a good one. I could have just cleaned up the cabinet and repainted it in place (after masking off the font panel). The end result, however, would have been far inferior to the professional finish that I now have. Plus, it would have been very difficult (perhaps impossible) to accomplish the level of work on the internal components documented above without first removing them from the cabinet.

New hardware was used to mount the components in the cabinet. The only exceptions were specialty items that were not available locally.

Reassembly of the cabinet begins
Cabinet ready for re-assembly

Day 10

Cabinet reassembly was completed today. All components have been mounted in the cabinet. It turned out great. Just what I had hoped.

Mounting some of the components proved to be a challenge, but all was accomplished successfully, with a minimum of delay.

The cabinet original finish included some stenciled legends. Those were lost when the cabinet was refinished. I attempted to find suitable stencils to duplicate the original legends. Unfortunately, no practical stencil set could be found that would allow letters and numbers of 1/4-inch in size, which would have matched the style of the originals. The smallest size I could locate (after some searching) was 1/2-inch, which is just too big.

The solution will be to develop a "nameplate" drawing that shows the locations of the major components. The nameplate will also include the manufacturing information (model number, date of manufacture, serial number, etc.). The nameplate will be located on the inside of the cabinet cover. So, when the cover is open, the information will be clearly visible.

And speaking of the cover, it was installed as the last step in the cabinet reassembly process. At some point in the past, an owner had drilled three holes in the cover, presumably to mount a mic boom stand. There aren't many options to eliminating those holes, other than just putting screws in them, which was the approach I took. With all of the mic mounting options available, it is disappointing that an owner would bring out the drill. It has been theorized that the chipped front end trim piece described above was the result of a mic stand affixed thereto. (Sigh...)

The three gray trays in the middle of the cabinet hold the program line amplifiers. They will be installed after the covers are refinished. At this point, the only components missing are the monitor amplifiers, as detailed previously.

I am now beginning to look closely at the front panel and develop a strategy for restoring it to new condition. I may go with a polycarbonate overlay, rather than attempting to remake the aluminum faceplate. Not sure yet. I have removed the aluminum U-shaped trim piece around the two VU meters. It will be refinished in the same black powder coat as the cabinet. Also, the meter lamp housing is rather beat-up. It will be refinished as well. Four 28 V bayonet-type lamps are used to illuminate the VU meters. The lamps also serve as a "pilot lamp" to indicate when power is applied to the console.

For the time-being, attention will shift to rebuilding the power supply, and after that, checking the front panel wiring.

Cabinet reassembled
Internal view of assembled cabinet

Day 11

Work continues to rebuild the power supply. This is a major undertaking. The project can be divided into three major stages.

Stage 1 was to repair the circuit board. As noted above, the existing board was in poor condition. Parts were missing and the board had suffered through some sub-optimal service over the years. All of the transistors were mounted in sockets, and unfortunately, some of the sockets had deteriorated. In one case, the transistor would simply fall out. Given this sad state of affairs, I removed all of the sockets from the board and direct-wired the transistors to the board. In addition, there were four zener diodes mounted in transistor sockets. I found this very odd. Here again, the sockets were not reliable and so they were removed. The diodes were soldered directly to the board.

The use of sockets is a bit of a mystery. Some boards in the console use this technique, and in others (such as the mic preamps) the transistors are soldered in place. There are two obvious explanations. First, the reliability of the devices was uncertain and so using socketed devices would allow for easy repair in a timely manner. Second, there was concern about device failure due to excessive heat during board construction and/or maintenance.

For modern circuit boards, most work is done using soldering irons rated for 25 W or less. Back in the day, however, soldering irons were big and hot. And then there were soldering guns. So, there may be some validity to the second theory. In any event, the sockets are gone and the board looks better for it.

Stage 2 will be to refinish the cabinet. The old cabinet was scratched and otherwise beat up. I'm not sure how it could have become so physically stressed while in the protection of the cabinet. Anyway, a trip to the refinishing shop will get all of the old paint off and a new coat of paint applied.

Stage 3 will be reassembly. Testing will come later, after initial work on the front panel has been completed.

While the power supply assembly is coming together nicely, I may still replace it with a modern IC-based supply. This is easily accomplished. Before going there, however, I want to get the original power supply back into operating condition, if possible.

Power supply circuit board, component side
Power supply circuit board, foil side

Day 12

The focus of today's work was the front panel. All of the wiring was inspected and cleaned-up as needed. In addition, all of the attenuators were opened and cleaned. The front panel knobs and attenuator trim plates for the 10 mixer channels were also removed in preparation for some serious work on the front panel.

It is evident from the condition of several of the attenuators that they had been serviced or replaced at some point in the past. In a few cases the wiring job left something to be desired. Those shortcoming have now been addressed and the wiring has been put back the way it should be.

Fortunately, the attenuators can be easily removed from the front panel (as shown in the photo), and they can then be cleaned without messing up the surrounding circuitry with over-spray from contact cleaner. All of the attenuators are in good mechanical condition. There are no obvious signs of damage. Contacts that are visible through removal of the back cover look good.

I have noted previously that some modifications have been made to certain parts of the console. That extended to the front panel as well. Fortunately, the changes were confined to the microphone input switches. Pads are used to adjust Mono/Stereo switching levels. For unknown reasons, two of the three pads had been changed. The close-up photo on the right shows one of the troublesome switches.

Fortunately, the switches are accessible and the correct resistors easily obtained. Work was slow and detailed, but now it's done.

All of the off-standard changes made to the console have been removed and the console is now in the as-designed state.

The need to customize a console such as this is understandable. However, considerable flexibility is designed into the unit, with most critical circuits (including the microphone inputs/outputs) available on one or more terminal strips inside the chassis. The modifications should have been made there, not on the front panel.

There are many drawbacks to these sorts of custom changes. First is that the changes are not documented. Or, if they were, the documentation has long since been lost. Second, attempting to improve on a design that has been used in a large number of installations over a long period of time seems dubious.

Enough complaining. I knew work would be required to get the console to the condition we wanted. And, now that those problems are fixed, we are done with them.

Front panel with one attenuator removed
Microphone switch issue

Day 13

Another trip to the powder coating shop brought back the cases for the Program/Audition line amplifiers. They were installed as shown on the right.

Also back from the shop was the right side cabinet trim piece. This, you will recall, is the piece with the chipped end. The cabinet looks very nice, and the trim piece (even though it has a flaw) will suffice for now. The only practical solution to fixing the chip is to replace the piece. This will require finding another Gates console of this series. Candidates include those shown in the Gates advertisement at the top of this page. The search continues, but at a low priority.

The last trim piece to be refinished was the one over the meter bridge, as shown in the photo. In the original design, this piece was anodized aluminum. That looked fine, but the finish really didn't match well with the aluminum front panels (upper and lower), which are anodized brushed aluminum. So, I had the meter trim piece refinished in the same satin black texture powder coat as the rest of the cabinet. I like the look.

The console, as built, uses 7 matching transformers (Triad A-21) for various functions. There is a position for an 8th device. I was able to find an A-21 on eBay for a reasonable price. After cleaning it up, I installed it in the cabinet. I have no particular need for the transformer right now, but it may come in handy later.

Other work today included mounting replacement Master Gain potentiometers on the front panel. When I purchased the console, both of the gain pots were missing. That is fixed now. I am also looking for suitable replacement knobs for the Master Gain controls. There are a couple of possibilities, which I am pursuing.

As the cabinet continues to look better, I am more convinced than ever that I will want to have the front panel aluminum pieces remade. In the case of the top panel, I can probably use the existing aluminum and have it refinished with new legends applied. (A thorough cleaning may also suffice.) For the lower piece, I will need to have the panel reproduced. With the three unneeded holes (as discussed previously), there is really no good option for fixing this, other than starting over.

I have removed the ten attenuator trim pieces from the front panel. They will be refinished and new legends applied.

Program/Audition amplifiers installed
VU meter trim piece

Day 14

The power supply rebuild project was finished today. As outlined above, there was a lot of work necessary to get the power supply back into operating condition. Aside from the cleanup and component replacements detailed previously, the cabinet was refinished and the circuit board thoroughly cleaned.

Upon completion of this work, the unit was powered-up for for testing. The unregulated 37 Vdc supply worked, but the 30 Vdc regulated supply did not. The trouble was traced to a faulty transistor, which fortunately was relatively common and a replacement easily found.

It was evident that some work had been done on the unit before I purchased it. The faulty transistor was presumably the cause of those earlier problems.

With the new transistor in the circuit, the power supply started up perfectly. When unloaded, there is a wide operating range, from a low of 20 V to a high of 36 V. The supply was set for 30 Vdc and run for several hours. There was no noticeable drift and no excessive heating of components.

Still to come is a nameplate for the power supply giving the operating ratings and connection pin out. This will be installed later, after the piece is produced by Metalphoto of Cincinnati, which I use for all polycarbonate overlays.

In the coming days, the power supply will be installed in the console and the various circuit boards powered up. I plan on doing this one board/module at a time in order to check the operation of each circuit. Keep in mind that the console has not seen powered operation for many years, so a go-slow approach is advisable.

Power supply external view
Power supply circuit board view

Day 15

Power on!

This was a big day for the console as the power supply was reinstalled and power was applied, most likely for the first time in many years. As planned, power was applied to one module at a time. As each module was connected, the current drawn from the supply was measured and compared against the typical operating current as documented in the user manual.

No problems were discovered, although two wires were left unconnected because it is unclear what function they serve. I'll figure that out later.

The power supply performed well under load. There was essentially no change in the output of the regulated supply from no-load to full-load. The board ran for a couple of hours to confirm that things were OK.

I did notice one issue that, fortunately, was easily addressed. The defective transistor discovered during initial tests was hot. None of the other transistors, including the TO-3 series regulators, ran hot. I added a small press-on heat-sink and the device then ran warm, but not hot.

It is possible that excessive heating caused the failure of this transistor in the first place years ago. In any event, I will keep a close eye on the supply—but so far things look good.

With power on, the VU meters light up. You've gotta love that.

While reinstalling the power supply, I took the opportunity to document the wire numbers for each module power input. This information may be useful later.

In the coming days, the performance of each module will be examined, and a full range of tests will be run.

Power supply installed in the console
Gates console with power on

Day 16

The first audio signals were passed through the console today, and preliminary tests were run. In addition, the functionality of all modules was confirmed. Frequency response met the published specifications, but a high noise floor prevented accurate THD and IMD measurements.

The noise was traced to the power supply. Additional filtering on the output of the supply helped (it also reduced the transistor heating noted above), but was not sufficient to solve the problem.

As it sits, the noise floor is down about 40 dB relative to the nominal output of +8 dBm. Additional work on the power supply is planned, notably replacement of the main filter capacitor. Unfortunately, this will require removal of the supply.

Despite the setback, it was great to have audio passing through the system, from mic input to line output.

Audio passing throug the console

Day 17

While troubleshooting the power supply ripple problem, I discovered that the connector for the left channel line amplifier was intermittent. This was not the cause of the noise problem, but it apparently was sufficient to cause the power supply to fail. With no input audio, each line amplifier draws about 100 mA. This intermittent connection evidently led to voltage spikes on the supply line that damaged a number of components in the power supply.

I had previously wondered why the transistors and zener diodes in the power supply were socket-mounted. Now I understand why. When the supply fails in this manner, it destroys multiple devices. The traditional troubleshooting method of replacing one part at a time is a hit-and-miss proposition here.

After spending a day trying to get the supply to work again, I decided to simply build a new power supply using modern devices. I settled on a design using the LM337 negative voltage regulator. The new supply is the same physical size as the original unit and has the same pin-out. It features greater output current capability, uses one-third of the parts, and is far more robust against failure than the original unit. Also, the supply is designed so it can be replaced in the field in minutes.

The new power supply is shown on the right. The design is simple and straightforward. An over-sized heat sink was used to ensure ample operating margin. The TO-3 transistors of the old power supply were not needed, and were therefore removed. The covers shown in the photo on the right are strictly for appearance.

Nearly all of the components of the new power supply are contained on the PWB. Connections to chassis-mounted devices and terminal strips are made via a Molex connector. The entire circuit board can be swapped out in minutes, making field repair much simpler and faster than with the old design.

It was my goal from the start to keep the Executive console as "original" as possible. I really wanted to get the old power supply to work, but at a certain point it is best to cut your losses and go in a different direction. One of the major problems is that circuit boards of 1960s and '70s vintage are very unforgiving of rework and repair.

Today I installed the new power supply and it works well. The noise problem is gone and the supply is stable

Rear view of new power supply
Front view of new power supply

Day 18

With the power supply problem behind me, detailed proof-of-performance testing was done today on the preamplifier circuit boards and the program line amplifier modules. With a couple of exceptions, all of the circuits met or exceeded their original specifications. The exceptions were limited in scope and will require some additional work. However, none are show-stoppers.

Most of the tests on the console are performed with an Audio Precision System One automated test set. The performance of each sub-assembly is being documented in an updated user/service manual that I am preparing. The manual will include all of the wire number information I have been able to collect during this project. Having a list of wire numbers and their functions has proven to be very helpful in the restoration work.

One item that is giving me trouble is the cue amplifier. That particular board has had a rough life, with considerable repair done over the years. I may remove the cue board and do some bench work on it. But, that project can wait for awhile.

With successful completion of the new power supply, I am beginning to work on designing a replacement circuit board for the microphone preamplifiers. My plan is to replicate the original Gates design, consistent with the availability of parts. I already know that the input transformer is going to be a challenge.

Testing the console

Day 19

The nameplate for the console arrived today and was installed. The nameplate (shown on the right) includes a diagram of the major components and connection points. It is made of brushed aluminum. The piece was produced by Metalphoto of Cincinnati, which I have used in many other projects for replacement front panels.

Also, the cue amplifier is working. The problem turned out to be a failed transistor on the cue amplifier circuit board. Basic functional tests on the cue system indicate everything working properly.

With the experience of repairing the cue amplifier board by replacing a plug-in transistor, I am beginning to appreciate the benefits of using sockets for the transistors. I would probably not build a new board with sockets, however.

During crosstalk tests on the microphone amplifiers, I discovered a curious modification that mixed the left and right channel inputs through a 20 dB pad when the channel was switched to STEREO. That didn't make much sense to me, and so I returned the circuit to the original Gates design.

In addition, a modification was found to the Network input that took the mono source and delivered the signal to both the left and right channels, but with a difference of about 3 dB. That didn't make sense to me either, and that circuit was returned to the as-designed configuration.

At this point, I believe that I have found and removed all of the changes done in the field over the years, and the console is back to the original configuration.

The design has been finalized for the replacement preamplifier circuit boards. A replacement input transformer has been identified that should provide equivalent performance to the original transformer, which is no longer available.



Day 20

Another big day for the restoration project. For the first time, audio programming was sent through the console and reproduced on the left channel monitor speaker.

After a long search, a monitor amplifier was located on eBay. The unit was in relatively good shape when it arrived. The circuitry was removed from the cabinet, and the cabinet was sandblasted and refinished to match the other modules in the console. The circuit board was thoroughly cleaned, and electrolytic capacitors were replaced as needed.

The monitor amplifier is shown on the right installed in the console. Testing has been limited to feeding program material to the console and listening on a speaker (which, of course, is the ultimate test of a monitor amplifier). A formal proof of performance will be conducted later.

The search continues for another monitor amplifier, which will complete the console.

The first of the new preamplifier boards has been produced and preliminary tests have been run. Final testing cannot be completed until the input transformer arrives (it was back-ordered).

A couple of troublesome issues were resolved today. One involved a level mismatch among the three output channels. That was addressed by modifying one of the VU meter pads. The other issue involved a significant level mis-match between two settings for the right channel line amplifier input. That was addressed with a modification to an attenuator pad feeding the input switch.

In both cases. the reasons for the changes and the parts used were documented so that an engineer at some point in the future will understand what was done and why.

Monitor amplifier installed in the console
Front view of the monitor amplifier

Day 21

The first replacement preamplifier board was tested and installed today (see the image on the right). Performance was very good, exceeding the original equipment specifications. However, like many initial versions, this one had a problem too. If you look closely at the bottom left corner of the photo, you will notice a couple of capacitors and a 5W zener diode. The lead of the zener diode extends to near the edge of the board. When the board is inserted into the card cage, the lead from the zener diode can come into contact with the card shelf rail, which shorts the component (and the V– supply) to ground.

So, another version of the card was produced, this time with generous clearance between components and the edges of the board. This is a four layer board. In the second version, the card edge finger connectors are placed on both the foil side and the component side, which doubles the connection surface. This is important since some of the mating connector plating has deteriorated over time. In addition, the new board is slightly thicker than the original, which makes for a tighter (better) match with the card cage socket.

The updated preamplifier board is shown on the right.

In order to get the best test numbers, it was necessary to change the values of some resistors in the input stage in order to accommodate the new input transformer. The transformer (Hammond 560G) is not a perfect match to the original. However, with the component changes it performs very well, easily exceeding the original equipment specifications.

Comparing the performance of the original board and the replacement board, the usual figures of merit (frequency response, phase shift, THD+N, IMD, power bandwidth, linearity, and noise) were closely matched. The major difference was input/output phase shift. The original board has a phase shift ranging from –30 degrees at 20 kHz to +30 degrees at 20 Hz, referenced to 1 kHz. The new board has a phase shift ranging from –15 degrees at 20 kHz to +30 degrees at 20 Hz, referenced to 1 kHz. Because of the differing phase shifts, an old board and new board should not be used in the same microphone channel.

New preamplifier board
Revised preamplifier board

Day 22

The replacement preamplifier boards have been completed and all 10 have been installed in the console (as shown on the right). If you look closely at the far right side of the card cage, you will see the original cue amplifier. A new circuit board has been designed for that amplifier and will be assembled within the next couple of weeks. As with the replacement preamplifier board, the replacement cue amplifier will be identical to the original Gates design, except for part substations where needed. The only other change from the original design is the inclusion of a resettable fuse on the V– input and some on-card power supply filtering on all boards.

In a major step toward completion, work on the front panel has been finished. As stated previously, the upper aluminum panel was in good shape, but the lower panel was scratched and had three extra, unused holes drilled into it. So, replacement of the lower panel was the only solution.

I used the vendor ProtoCase to produce the piece. It was a very difficult project because every hole needed to be exactly duplicated on the new piece, or the whole thing would be useless. I developed an AutoCAD drawing of the lower panel, along with detailed dimensions and the necessary labeling.

When the panel arrived, it was very close. Unfortunately, it was not close enough. I could have made it fit by drilling-out some of the switch holes, but that was a poor solution. Instead, I made the necessary changes to the AutoCAD file and the vendor produced another version. This one was perfect.

The finish is brushed aluminum with a clear anodized finish and lettering silk-screened onto the panel. The upper and lower panels look almost identical. Unless you examine them closely, you wouldn't know that one was produced 50 years earlier than the other.

Another project that ProtoCase took on was to refinish the round dials for the fader knobs. They were sandblasted and powder-coated, and then the lettering was silk-screened to make the finished piece.

The original fader knobs were in good condition, needing only a thorough cleaning. The colored inserts added by some stations had faded over the years. They were all removed, except for two silver inserts and one gold insert, which were placed on the microphone channels. I will probably have the inserts reproduced in a couple of colors, but that can wait until just before the board goes into service.

Preampllifier card cage
Console with front panel completed

Day 23

As mentioned previously, the Executive console requires an external ac power supply to function. Three 28 V ac circuits are needed—one for the card cage and program amplifiers, and one each for the right and left monitor amplifiers. The ac supply was not included with the console when purchased on Bay. Fortunately, the requirements are easily met with three low voltage transformers.

The original supply was modest in construction; essentially a panel with transformers mounted on it. For the rebuild, however, I decided to produce a more polished supply, as shown on the right. The 19-inch rack-mount chassis was produced by ProtoCase using their ProtoCase Design software. The end result was very good.

I maintained the style of the Executive console with a brushed aluminum front panel and black textured powder coat finish.

The three independent 28 V ac circuits are fed by a power conditioning system that includes surge limiting, filtering, and overload protection.

The ac power transformers are mounted external to the console in order to reduce hum in the system. The supply is typically mounted in a rack cabinet near the console. Separation of up to 10 ft is easily accommodated.

The chassis designed for the ac power supply will serve as the starting point for the cabinet of two future projects. The first will be a distribution amplifier and the second an AGC/limiter. Both are patterned after Gates Radio products of the early 1970s. They will serve to complement the Executive console.

AC power supply cabinet
AC power supply rear panel

Day 24

Work was officially completed today on the new preamplifier boards. All 10 are installed and working correctly. Performance meets or exceeds the original Gates cards. The new power supply board also works well, easily handling the current load with all preamp cards installed.

While checking the operation of the microphone channels, I was surprised to find another maintenance error from the past. (After all these months, I thought I had found all of them.) There are three stereo microphone mixer channels. The channels can optionally be switched to Mono, where the Left channel signal is fed to both program channels. While checking the new preamplifier boards, it was evident that the Mono circuit was not functioning properly on Channels 2 and 3. After several hours of troubleshooting, I found that the mixer attenuators for Channels 2 and 3 had been wired in reverse, with the Left channel feeding the Right, and vice versa. Both attenuators had been replaced at some point in the past, and the wiring error was presumably created at that time. Regardless of when it happened, now it is fixed.

Audio console under test

Day 25

The replacement cue amplifier circuit board was completed today and installed in the console. Like the new preamplifier cards, the cue amp is functionally identical to the original Gates board. Performance of the two cards is very close. Specific changes to the original design include: 1) power supply filtering on the card, 2) inclusion of a resettable fuse on the V– input, and 3) modified frequency response.

In the original Gates circuit, frequency response is rolled off sharply below 300 Hz and above 6 kHz. This was done in recognition of the primary function of the cue amplifier—voice communications. For the new card, the response curve was flattened somewhat to provide improved fidelity. The trade-off is slightly lower overall gain; however, this is not an operational issue since the cue circuit has ample gain.

The new cue amplifier board is shown on the right. Note the oversized heat sinks on the two output transistors. The original heat sinks were rather modest in size, and in bench tests one of the output transistors on the prototype board failed during power bandwidth testing (this testing mode pushes the operating limits of the circuit). It is not easy to find heat sinks for TO-8 devices, but a search on eBay did the trick.

In the middle photo, an aluminum shield can be seen mounted above the input transformer. An examination of the photo shows a plug-in relay directly opposite the input transformer. This is the intercom Talk/Listen relay, which puts the cue amplifier output contacts adjacent to the input transformer. The shield prevents feedback and noise from impacting operation of the cue circuit.

The bottom photo shows the completely rebuilt card cage, which contains ten preamplifier boards and the cue amplifier. When fully loaded, the card cage pulls about 300 mA from the power supply (200 mA from the 30 V regulated supply and 100 mA from the 37 V unregulated supply).

The addition of resettable fuses on all circuit boards is intended to avoid a complete shutdown of the console in the event of a failure on any one board. This is very important, of course, for on-air reliability.

The value of the resettable fuse was demonstrated during initial testing of the prototype cue amplifier board. As mentioned above, one of the output transistors failed during testing to determine the maximum output capability of the circuit (power bandwidth). The resettable fuse did not prevent the transistor failure (that was caused by excessive operating temperature) but it did prevent collateral damage caused by the failed transistor.

In a previous failure of the original cue amplifier board, two resistors in series with the output transistors failed rather spectacularly when one of the output transistors failed. The resistors, in fact, left burn marks on the board as evidence of the problem. Now, however, with the resettable fuse in place, the current draw was limited and damage to additional components was avoided.

New cue amplifier board
Cue amplifier installed in card cage
Rebuilt card cage assembly

Day 26

Thanks to a lucky find on eBay, I was able to repair one of the Audition/Program lever switches on the front panel. The Channel 3 microphone input worked fine in the Program position, but not in the Audition position. The cause was a broken element within the lever switch. This type of switch is typically quite reliable; however, this one had failed at some point in the past. Someone had attempted to repair it, but the fix did not hold.

I was able to find a similar lever switch on eBay, and because of the structure of the switch, replacement of the broken element was possible. This was, admittedly, a long-shot, but fortunately, the repair job went very well.

Meanwhile, work has begun on replacement monitor amplifiers. As mentioned previously, the monitor amps were missing when I bought the console on eBay. I was able to find one monitor amplifier, but of course two are required for stereo. So, replacement units have been designed (based on the original Gates units) and are being produced.



Day 27

The first of two replacement monitor amplifiers was completed today. The circuit is identical to the original Gates M6108A monitor amp, with some updates. The amplifier board is shown on the right undergoing performance testing on the bench.

The new version of the amplifier includes an optional circuit intended to limit current through the output transistors when the unit is over-driven. The current-limiting option was included in some later versions of the M6108.

The completed unit is also shown. The cabinet is the same physical size as the original Gates product, in order to fit into the Executive console. After testing has been completed, a second unit will be built. The one original Gates monitor amplifier will be taken out of service and retained as a replacement device, should it be required at some point in the future.

The cabinet for the replacement amplifier was produced by ProtoCase, using their design software. The results were very good. Improvements on the original cabinet design include large heat sinks for the TO-3 style output transistors and ventilation for the TO-8 driver transistors. Connection points are identical to the original amplifier in order to make installation in the Executive console straightforward.

The additional cooling of the output devices is particularly important for performance testing at full power, which generates a large amount of heat in the output transistors.

The new circuit board is sized to be an exact replacement for the original Gates board. The updated board, thus, can be used either to refurbish an existing M6108 or to build a new unit.

In parallel with work on the monitor amplifier, a replacement upper front panel is being designed. As noted in a previous blog entry, the original upper panel is in relatively good shape. The new panel is being produced in order to change some of the channel assignments. This is strictly a labeling change; none of the circuitry will change.

Monitor amplifier on the bench
Replacement monitor amplifier chassis

Day 28

I have finished a first pass on the replacement upper front panel. A representation of the panel is shown on the right. The two large holes in the middle are where the VU meters go. For reference, the lower panel is also shown.

My plan, at this point, is to have a new panel made, rather than have the existing panel refinished and relabeled. By the time I ship it off to the vendor and they prepare it for finish and printing, the cost of using the existing panel will match (or perhaps exceed) just starting from scratch.

Upper panel of the Gates Console
Lower panel of the console

Day 29

The new monitor amplifiers were installed today. This completes work on all of the major sub-assemblies. Minor repairs will be taken on as identified; however, all circuits are now installed and working correctly.

After the replacement upper panel is produced, wiring for remote start functions will be installed. The system will provide contact closures when the turntable channels are switched into Program or Audition. This function will be accomplished using available contacts on the channel lever switches.

After the console has been completed, work will commence on a stereo turntable preamplifier. Two preamps are planned, with the possibility of a third.

In a parallel track, the studio that will house the Executive console is being planned. Construction of necessary furniture is expected to begin in December 2017.



Day 30

With installation of the replacement upper front panel, the console is ready for service. At the beginning of this project, I estimated July 2017 for completion. So, I met the project time-line. Having said that, I have several other projects related to the board, including:
• I am working with FastSigns to reproduce the colored circular inserts for the mixer channel knobs.
• Rebuild the three line amplifiers. Thanks to some recent work, all of the line amps now meet the new equipment specs. However, the noise performance is a bit lacking, and they are the only active circuits that are original; that would make them about 50 years old. I have ordered parts for the first of two stages of work. This project should be completed by the end of October.
• Build two stereo turntable preamps based on a classic Gates design. That work should be completed by the end of November.
• As time permits, I plan on checking each attenuator (mixer fader) and cleaning them up as needed. All 10 are in good condition; however, they require service from time to time. I have found two replacement attenuators and refurbished them as spares.

So, the revised target date for having things ready to go is Thanksgiving.

As a separate project, I will probably build a stereo automatic gain control (AGC) unit using '70s vintage Gates units that I purchased some time ago from eBay. This is somewhat of a science project. It will be the last element of the Executive audio system. I expect to complete this by the end of 2017.

Front view of console

Day 31

Progress continues to be made on the updated line amplifier modules. Shown on the right is one of the completed units. There are three such modules; one each for the left channel, right channel, and audition channel.

The line amplifier module is made up of two circuit boards: the driver and the output. The new boards are the same physical size as the originals, and function the same. The major difference is the use of plug-in Molex connectors for the interconnecting wiring. This makes for easy service, if required.

In addition to replacing the circuit boards in all three modules, the plug-in connectors were also replaced. In a couple of instances, the contacts had deteriorated over time. Fortunately, exact replacement connectors were available. In one case, the mating receptacle on the mounting tray was replaced as well.

A replacement cabinet for the program amplifier was designed, but not produced, since three of the original modules were available. Should the need arise, however, a replacement cabinet is ready to go.

In the course of building replacement circuit boards for the console, I have in all cases built a spare board. The cost increment to build the additional boards was small, and having spares on hand going forward makes it possible to return the console to service quickly if a failure occurs.

Side view of completed program amplilfier
Side view of completed program amplifier

Day 32

In a lucky find, I was able to locate exact replacement switches for the upper front panel. These two-position lever switches are used extensively on the console (the entire top row). The switches have self-wiping contacts that tend to self-clean with use.

Over time, some of the switches had been damaged or otherwise were in poor condition. The main problems were with the three microphone channels, which had been modified in the past (as documented previously). The reliability of a couple of the switches was marginal, and so all six microphone input switches were replaced.

The new device, made by Electroswitch, is an exact replacement. The mounting holes are identical. The switches are available by special order only, and are rather expensive. However, having switches available for replacement is very important since repair of the device is quite difficult.

The photo on the right shows four of the new Electroswitch devices installed in the console.

Final steps in the Executive audio console project included a complete proof-of-performance for the unit and detailed documentation of major functions. A part of this effort included confirmation that all signal switching systems worked as intended, and that all levels were within specifications. Some minor fixes were made here and there, but largely everything checked out perfectly.

Internal wiring view

Day 33

Work on the Gates Executive Stereo Audio Console is now essentially completed. The unit is fully functional, and all active circuits have been updated. This project started off with no firm time line or budget. As it turns out, the time line was almost exactly one year. As for the budget, well that was a bit of a surprise.

Looking at the big picture, I have kept detailed records on what each element of the rebuild project has cost. The following represents the bill of material (BOM) costs, not including shipping, tax, time, labor, and NRE expenses (e.g., prototype boards and remade parts).
• Cabinet/chassis work = $1125
• Upper and lower front panels = $1100
• AC power supply and 30 V regulated power supply = $1749
• Preamplifier = $158 per board for a run of 10 boards
• Program amplifier = $605 per unit for a run of three
• Cue amplifier = $304 per board for a run of two
• Monitor amplifier = $498 per unit for a run of two
Frankly, I have been stunned at how much this stuff has cost. The major expenses are the cabinets (for the main chassis, AC power supply, and monitor amplifiers), circuit boards, and audio transformers. Purchasing the Executive console on eBay was the cheap part!

These expenses do not tell the entire story. The NRE costs have been significant–on the order of 50% above the production costs.

Still, the time and money have been well spent. The console is in superb shape and the studio where it will reside is under development.

Console in the shop