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Author Topic: Restoration of Gates M-5078 Commercial HF AM/CW Transmitter  (Read 8929 times)

Posts: 214

« on: April 29, 2012, 06:49:09 PM »

Hello All,

The link below is to an article about the Restoration of a Gates M-5078 Commercial HF AM/CW Transmitter. This transmitter was built by Gates Radio in 1957. Gates was known primarily for making broadcast transmitters. During the 1950's they also produced several SW transmitters for various commercial HF markets. Many of the types of endeavors that needed this type of long-range HF communications was mining, forestry, oil exploration, news media, remote scientific exploration, and others. This radio operates on all the amateur HF bands as well. All components in this radio are rated for CCS, so in theory (and probably in practice), this radio could stay on transmit for 24/7 and not suffer any ill effects.

It's a 50w input class transmitter, perfect for driving most amplifiers on AM.

This article talks about the specifics of this radio, and also has tons of useful information which can be used to restore any boatanchor or vintage radio; including painting techniques, making new decals for parts, and more.

The article is ongoing and is not yet finished (neither is the radio restoration) so bookmark it and check it out from time to time.

This is the link:


John LeVasseur. W2WDX
« Last Edit: August 24, 2015, 11:38:28 PM by W2WDX » Logged


Posts: 3135

« Reply #1 on: May 01, 2012, 06:28:50 AM »


Very nice work. Your attention to detail outlined in the article were the same lessons
I was taught in 1970s, by many Elmer's.  I also appreciated restoration tips (update on traditional cleaners I use),
I use TunerLube more than plain DeOxit (I use WD40 used for household work/door hinges, not electronics).

Since I grew up within an hour drive of the Quincy, IL HQ and plant -- I had opportunity to tour the plant on various occasions.  
I did not remember this model, but many of those parts are familiar from the larger commercial broadcast products.  The US broadcast transmitters were always small, compared to some of the high power international SW transmitters they built in 1960s and early 1970s.

Look forward to you decal offerings for other restorers.

« Last Edit: May 01, 2012, 06:36:34 AM by W9GB » Logged

Posts: 4941

« Reply #2 on: May 02, 2012, 08:05:48 AM »

Very nice. It helped that the rig was in such good condition.

A couple things.

Assuming you had to replace the oil cap, what would you use for a 1uf size? Polypropylene?

I use Krud Kutter on the front faces. After the crap comes off, I then use auto car wax because it is least abrasive. The buffer can remove paint. Seems to work well.

On refinishing the transformer. After stripping, I use a automotive etching primer, then a filling primer. One etches, and one fills the pits. The wetsand with like 800, and then finish. Nice thing about the filling primer is that if you screw up and use too gritty a sandpaper, you can start over.


Posts: 8085

« Reply #3 on: May 02, 2012, 08:33:44 AM »

Any ideas on date of manufacture? Obviously after 1953, of course.

Posts: 2080

« Reply #4 on: May 07, 2012, 01:20:51 PM »

Very nice, John.  I got my feet wet with producing inkjet and laser decals while attempting to make authentic-looking markings for some R/C aircraft I built.  Then I went on to produce some control decals for my restored Philco Cathederal that I could not find commercially.  Lots of trial and error.  But now I'll apply some of your pointers and might even take some of the old decals off and remake them.  Thanks for the detailed article.  Count me as interested when you find time to get your decals ready for market.


Terry, WØFM

Posts: 214

« Reply #5 on: May 18, 2012, 01:28:57 AM »

Hi again,

I have been busy restoring radios for the business, so I haven't had much time to work on the Gates lately (or the article) as of late. I will return to it before the end of May (2012) and finish up the article. Stay tuned.

To answer some of the questions, this particular radio was manufactured in Sept. 1957. It appears that Gates made several SW transmitters intended for commercial SW use during this period. This was the smallest one they made. Some were what we normally expect from Gates Radio as far as size. The HF-20 was a 18kW output (carrier) transmitter that was 5 racks, 210" wide, 49" deep & 78" high at 16,000lbs. Typical Gates! Another was the 1 rack HF-1 1kW transmitter. However, these were primarily for broadcast use on SW, and didn't contain microphone inputs (line input only) and no PTT.

Then we have the smaller units. These were complete self-contained transmitters containing mic inputs and PTT functions. The largest was the CMW-1 which used pair of 100TH modulating a second pair of the same. It was very conservatively operated at 700W input, although it could be run as high as 1kW output with this tube compliment. The next was the CMG-1 250W output (carrier) using a pair of 810's modulating a a pair of 4/65A's. It had a built in mic input, PTT and a self contained Gates Audio Limiter. A very nice transmitter. Both of these were large floor standing racks.

Of the smallish types, in addition to the radio I have here, there was a 65w input M-5569/5570. This was a transmitter (5569) that vaguely resembles a Johnson Viking I in appearance, but also has a separate power supply/modulator of the same size (5570). Unlike the radio I have here, the two units can be rack mounted in a standard 19" rack, but do also come in their own metal Gates racks. This was a Pair of 6146's modulated by the same. The modulator had a built in compressor with a threshold setting & gain adjustment as well as metering for the amount of downward compression. Nice feature!

Many of the components used in the M-5078 are off the shelf Gates parts used in the exciters for its larger transmitters, so the duty cycle on this little transmitter is, well ... crazy high! I did some calculations and on some parts, the maximums on some parts are only at about 20% (the fixed capacitors on the loading, for instance.) However I do not think audio fidelity was of a primary concern for this market, unlike the broadcast products.

The modulator does not use any "clippers" or other sort of tricks to limit modulation peaks, which is good. However, the audio bandwidth is limited to about 300-3kHz, through the use of "filtering" in the audio section in the form of High-pass & Low-pass sections. It was common in this period of high traffic on the HF bands to limit this, not to mention tighter restrictions by the FCC then exists today. I will most likely broaden this slightly by changing some of the values of coupling caps and possibly wrapping some negative feedback into the modulator to reduce distortion artifacts, which is probably at around 5% in the current circuit. I will also probably play around with the gain on the modulator to recover any loss incurred by using the feedback. But will first proceed with circuit as originally designed by Gates before making mods of this type. I should easily be able to achieve a flat response of about 100-5kHz with distortion at about 1-2% @ 100% modulation when all is said and done, which is more than sufficient.

This thing did have quite a bit of tinkering done to it, as it turns out. I have not mentioned this yet in the article, since I am only now at the point in the restoration of testing all the components. I'm finding numerous changed values on the components. While the radio worked fine, the changes made were ... well ... OK, but made the radio more like an amateur transmitter in performance, and certainly not CCS. The choices for duty cycle ratings were marginal at best, and were most likely "junkbox parts" to make the radio functional for the Hammy Hambone who did the work. The values selected were also "best guess" or whatever was on hand, like the microphone input using a higher than normal value for a low impedance mic. The value wasn't even a compromise to allow for a high impedance mic. It was just a high value, too high in fact. Also the RF choke was removed completely off the mic input.

The PTT function as added, while functional, was done poorly. I will correct all of this and make it more inline with the original Gates CCS design criteria. The PTT mod control wires ran all over the chassis, and were not incorporated into the existing harnesses. They caused quite a bit of trouble when the modulator/PSU chassis was taken apart. Each is a separate chassis, connected together via a terminal strip. The PPT wires could have been routed through the spare terminals available. Alas, they were just directly wired haphazardly and tied off to random things underneath. Also the wires were not high enough gauge for the current they are carrying, and were of a different type (teflon insulated solid wire.) While it is just a personal preference, I will change this to a higher gauge cloth type wiring like the original Gates wiring. The relay was also a junkbox component. I will also use a much smaller (and quieter) relay and eliminate the added unnecessary transformer for this application. The relay used has a low voltage coil (24V) so a transformer was needed. Again it was probably what was on hand. I will change it to a 120VAC relay and eliminate the transformer completely.

The decal thing is quite fun. I cannot tell you how nice a radio restoration looks when you have the decals redone as well. It just puts it over the top and makes the radio look brand new. The "icing on the cake", so to speak. The decals on this radio came out very well, and I can't wait to "brag" about it, Grin Seriously, I just really like doing these types of details and get very happy when it all works out. I have the images and promise to show the technique, as well as the finished product in the article very soon. My hope is to benefit everyone who would like to do this as that extra step that puts their own restoration project over the top.

As far as the paper oil caps, I am not a big fan of "Orange drops" so popular these days. Several reasons, very large and the leads are not true axial, which makes for sometimes difficult placement within the existing circuitry. Also I find a large variation in values, sometimes even beyond the rated tolerance. What I do use are axial lead tubular polypropylene (the little yellow ones) in most cases to replace oil/paper caps. I do test the components out of a large lot to find the nearest value as a QC thing. However, I do find the typical poly's made available are usually within tolerances, unlike the Orange Drops.

The etching primer is a great idea, but the most important thing to do is to make sure you stabilize the metal underneath. Even sanding away all the visible rust or corrosion doesn't mean it isn't still there on a molecular level. Converting this surface is essential to prevent rusting from starting over underneath the new primer & paint.

I have used TunerLube as well, however I do find it has a tendency to harden up over time as well since it does use some non-synthetic petroleum products. But it isn't as bad as some the other choices used by some.

Hope to have the article updates coming soon and thanks for the kudos folks.


John, W2WDX


« Last Edit: May 18, 2012, 01:39:08 AM by W2WDX » Logged


Posts: 214

« Reply #6 on: June 08, 2012, 11:47:16 PM »

A couple things.

Assuming you had to replace the oil cap, what would you use for a 1uf size? Polypropylene?

I have been very busy with the business as of late so sorry for the late reply.

To be more specific, I like to use Vishay Sprague 730P type metalized polypropylene capacitors to replace these types of paper/wax caps.  In this case I will use a 730P105X9250, which as you can tell from the number is a 1uf 250vdc 10%. The case is 1.25" in length and about .5" in diameter, slightly smaller than the original cap being replaced. These are axial lead, available in capacitance from .0022 to 10uf, 100-630 WVDC, in 20%, 10% & 5% tolerances.

Here's an image of the cap:

Here's a link to a spec sheet:

These are very high quality, stable and not susceptible to moisture.

I hopefully will be working on the article a bit more this weekend.

John LeVasseur, W2WDX
« Last Edit: August 24, 2015, 11:41:21 PM by W2WDX » Logged


Posts: 214

« Reply #7 on: August 24, 2015, 11:43:31 PM »

I just redid all the links on here since most were on my business website which I closed down due to an auto accident. Now that I recovered after nearly two years of physical therapy I intend to return to the restoration of this transmitter and the related article. I have migrated the article to my W2WDX web site. The new link has been updated in the OP.
« Last Edit: August 24, 2015, 11:46:58 PM by W2WDX » Logged


Posts: 214

« Reply #8 on: September 30, 2017, 09:05:27 PM »

Hi all,

So the restoration continues ... been busy in the pro-audio world lately, mainly restoring vintage tube gear for that. I also have been building custom water-cooled PC's for the gaming market. You know ... gotta make a living somehow! LOL!

Over the remainder of this year (2017) I will be posting regularly to this article, hopefully having this radio restored by years end. It been a long road, having started this restore back in March of 2012. But this one I have no reason to rush and want to do it correctly since I am beginning to think this is the only surviving example of this model of Gates transmitters. Currently I have been working on the audio section, deciding to not only completely replace everything with carefully matched NOS components, but also making slight modifications to allow for more modern operating practice. (I do intend on making this transmitter my primary HF AM rig).

The most recent update of the article includes some thoughts on the audio circuit, as well as some notes on a conversation I had with a semi-retired individual who still works part time for GatesAir who claims he was a tech who final tested these transmitters in the early 60's at Gates. Being involved in customer support on "legacy" products, he was able to find all the original production drawings and internal parts lists, as well as an original user manual which are currently on their way to me. More details of this very interesting conversation are contained in the article (page 9). Also on this page, is a full description of the circuit design I finally decided upon, with new images coming soon. (Having problems with getting my images off my Canon SLR onto this old MacBook I've been using as of late).

While at my site you should check out some of the other restoration and modification articles on a variety of boatanchors I have used over the years, including a recent one on the restoration of a very rare Hammarlund HQ-110AC-VHF. The full listing of all my articles can be found at where you can also find links as well for the article on the Gates mentioned above.


John, W2WDX

« Last Edit: September 30, 2017, 09:09:05 PM by W2WDX » Logged

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