I’ve serviced and modified many Altec 43X-series compressors over the years, but I think this may be only the 2nd one I’ve built entirely from scratch. Styled more like a Federal AM864, this unit incorporates many of the tweaks and modifications that I have come to like in these machines. Here are some images of the build.
Couple of things to point out in the photo above. Note the larger “Octal” tubes (6X5 rectifier and 6SN7 output amplifier) on the left side. I like octal tubes, as the larger sockets are easier to work with, so space-permitting I tend to use them. The original 43X used a solid-sate rectifier (with a voltage doubler) but I used a more conventional full-wave supply with a rectifier tube since it suited the look better. The 6SN7 output tube was a nice choice as there are so many variations of this tube available. It’s a direct sub for the 6CG7 in the original Altec.
Also note: behind the meter is a ‘meter null adjust’ pot. I can’t recall how this was handled on the original Altecs, but this mod is a common one shown on many internet schematics of the 436. Also note the large pot to the left of the meter. This is the Gates Sta Level output trim control (-6 to -14db cut) that I detailed on this site years ago. A worthy and necessary addition!
You can also see the enormous output transformer in the center: a massive potted unit built for Daven, likely by UTC. originally built for hi-end test gear, it is ultra hi fi and handles more level than this thing will ever see.
Above: some detail of the meter. I was motivated to build this thing solely because I found that original Altec panel meter at a hamfest for a buck. Seemed like it needed a 2nd life… Also check out that finish on the panel! That’s about 6 layers of paint and 3 layers of clearcoat, sanded between each coat. The knobs are all NOS 1960s DakaWare, acquired from Park Distributors in BPT CT (RIP).
Above: the UTC A18 input transformer, which has similar specs / ratio to the Peerless plug-in unit that an original Altec would have been outfitted with.
Above: the completed unit on the bench. The input pot is a really nice dual-gang 50K 1-watt sealed unit; I got several of these from Park before they closed. I cant imagine that any pot like this is available today for under $50. Good find. Running the length of the unit to the immediate right of the turret board is the heavy copper ground buss. Every ground in the machine connects here, and only here, and the ground buss meets the chassis at only one spot – the input jack. I swear by this construction technique. I’ve rewired a lot of old cheap tube guitar amps with this addition and the improvement in noise floor is remarkable.
9 replies on “Altec 436C style compressor build #2”
Great build – it looks amazing!
I’ve just built myself one but sadly the original Peerless input transformer I bought for it doesn’t appear to pass signal correctly. I have an UTC A18 lying around and noticed that you used one for your build. What are your thoughts on it? Have you noticed any issues with headroom at all?
Thanks,
Matt
A18 works great. Rated at +15 but i suspect it can pass more. i havent heard it distort yet. In the past i built these with +8 UTC ouncers and those are not ideal. A series should be fine. good luck.
Your builds look astonishing and exactly in line with my tastes. But what I don’t see is whether or not you build these for anyone other than yourself? I’d love to know!
Hello. thank you Vincent. I don’t take orders at this time. I do sell the completed pieces however. This particular compressor has been sold.
That’s good to know. The combination of the old and new (and the reliability that should engender) is exciting. Amplification is the touchiest aspect of vintage equipment — the most dangerous, I suppose, and yet the most coveted. What became of your Western Electric 43A Homage Amplifier? Spectacular stuff.
Oh, and a new build of the Altec 128B, preferably as a stereo rather than mono tube amp…. that would be exceptional!
hi.i have always wanted to build 128Bs. I have not been able to because i cannot find data on the ratio of the feedback winding in the output transformer. I believe the OT was a proprietary ALTEC part so i don’t think this data is found in any catalog. If would require that someone disconnect the OT in a 128B and then measure the turns ratio. If you have this intel, pls lmk. thanks.
I’ll do some digging. I know some very technical people who have 128Bs. They might know the magic formula… or be willing to do what you mention to get the ratio. I’ll let you know what I find.
Did you follow the original schematic for the design?