I even looked in my copies of the old Ham Radio Yellow Sheets Ham Radio Buyers Guide and nothing.

    Fortunately, after posting an "information wanted" ad on QTH.com, a very nice gentleman N4CH came through. Herman is a wealth of knowledge and below is listed his info gleaned from several emails.

     Thank you Herman for taking the time to share your knowledge.

     From Herman N4CH:

    The Varitronics PA50A is a pretty rare 2 meter amp, made about 1970-71. Specs are 10 watts in, 30-40 out, with a PNP RF transistor in an internal "floating ground" configuration, designed to run off 13.8 volts. I believe these amps were made in Phoenix, Arizona, to pair up with their Varitronics IC-2F 2M FM radio (made for them by Icom......Icom's 2nd 2M radio, actually). These were among the first solid-state amplifiers ever made designed for 10 watts drive. Not many were sold. Be careful with it........if you blow the PA transistor, you will probably never find another similar one. You are correct regarding RF sense keying.......good for FM only (NOT an all mode amp).

     It is definitely designed to be driven with 10 or so watts. They ran a few ads in 73 and QST, but the meter shown in those photos had a numbered scale (0-50 or 0-100, maybe). The amp I have (as well as the one or two others I've seen) have a meter with nothing more than a stripe running horizontally, and a simple line at about 2/3 scale. I believe this was the only amp they ever sold (I've never seen a PA-50 or an ad for same). It was about this time that Varitronics also ran a few ads and actually sold a few handheld radios for 2M FM, their HT-2, which was HUGE. Ugly, gray plastic, and only 2 channels........and a watt and a half out (on a good day), also made for them by Icom. Back in this period, Varitronics was the sole importer for Icom, and everything they sold (except for this PA-50A, which I think had a sticker price of $129.95) was made for them by Icom (known as Inoue Communications back then). Varitronics was in business for only a year or two.

     One would think that Varitronics may have made at least 200-300 of those amps, but it's anyone's guess whether or not they started at serial # 001. I go to a LOT of hamfests (have been doing so for almost 50 years), and I've only seen two of these amps (and that includes Dayton every year for the last 31 years). The PA-50A was built a lot better than most of the other amps of that era. The only shortcoming was the heatsink; the only heat-dissipating area is that large internal aluminum slab, along with the front and back panels. Some fins would have been good.......these amps run pretty warm, as I recall. Be careful when you tune it up. As with most such amps, it's a good idea to have a dual directional wattmeter (such as a Daiwa 0-20/0-200 watt cross-needle VHF one) inline between the 10 watt driver and the amp's input, along with a good dummy load and wattmeter on the amp's output, so you can tune the input matching caps for minimum reflected power while looking at drive power going into the amp, along with its output power. If you can have a spectrum analyzer (to look for instability) that might be invaluable. As I recall, the PA-50A can easily take off and oscillate if the output caps are badly mistuned, and that can lead to damaging the PA transistor.

     If you can find a Varitronics IC-2F (the 2M, 10W, 6 channel radio they sold for about $400.00 new back then), it and the amp make a nice-looking matched pair. Those do still show up from time to time. Icom also supposedly made a look-alike 6 meter FM radio (the IC-6F) back then; I've been looking for one of those for over 40 years. Never have seen one, but they did run a few ads.

     You found a nice one. I just looked at the photos of the one you have. Turns out my "nicer" one also came with a box. The other one I have I got as a "parts" amp; the PA transistor was blown, and after spending a year or two looking for an unobtanium replacement, I went ahead and made some extensive mods, and reversed the floating positive ground setup, and replaced the original (PNP) transistor with a more conventional NPN device (think I used a TRW PT8874, which looks like what was in there originally, but is a 10W in, 40W out NPN device). Very difficult to do........beginning with removing that vertical piece of PC board that shields the input/output. Back when these amps were designed, the first such amps used PNP transistors, and since everyone's car by then was negative ground, complexity was raised to put a "floating ground" circuit in there. If you take a close look, you will see that the ground plane on the amp's circuit board is + 13.8V as referenced to the chassis. The only other 2M ham amp I've ever seen this done is Regency's AR-2, which used two transistors in parallel.......it came out as a companion to the HR-2 just after Varitronics did the PA-50A. It is a VERY heavy amp.......it has a thick, solid copper heatsink inside. Midland made a 12 channel, 25 watt 2M FM transceiver in the early 70s where the last 2-3 TX stages used this same technique.........finding exact replacement transistors for all these products is next to impossible.

     I don't think Varitronics ever made a 6M amp, and it's probably almost certain they never imported any IC-6F 10 watt 6M FM radios (which they briefly advertised) either.