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Help Identifying Tube Amp Chassis
#1
Hi All!

I picked up this amp chassis for $20 today. No tubes or documentation included. The only markings are a stamped circle with "32E" inside. The over-all circuit appears to be push-pull using some kind of octal power tubes like 6v6, 6l6, etc (pin 1's unused, pin 3's [plate] tied to one side of opt primary, pins 2 and 7 heater). Here's where the odd comes in. The screen grid pins (pin 4's) are tied to the cathodes (pin 8's), which are tied to what appears to be a filter capacitor positive voltage node. Both grids are tied together, and go to the 9-pin octal style socket. The power supply uses solid-state rectifiers, and appears normal enough. There appears to be both main B+ and a single-diode negative voltage source, and there is what looks like a bias POT with no guts which is NOT tied to the power tube grids. I can't figure out what exactly its purpose was. There doesn't appear to be any specific grounding scheme, as some grounds go to chassis, while others tie together in a semi-star style. My gut instinct is to just gut it and start a build from scratch. However, if this is a bit of a rare amp configuration worth a possible resurrection, I'd consider that undertaking.Any help/input appreciated!


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#2
Hi Guys

The output tube wiring looks like 7591.
1. nc
2.h1
3.a
4.g2 optional
5.k,g3
6.g1
7.h2
8.g2

RCA made both tubes and finished products. For the latter, they often used variations of standard tubes with odd pinouts so there would be a captive market for some of their tube range. It is likely the driver tube is also one of these non-standard pinout tubes.
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#3
(06-12-2023, 12:00 AM)K O'Connor Wrote: Hi Guys

The output tube wiring looks like 7591.
1. nc
2.h1
3.a
4.g2 optional
5.k,g3
6.g1
7.h2
8.g2

RCA made both tubes and finished products. For the latter, they often used variations of standard tubes with odd pinouts so there would be a captive market for some of their tube range. It is likely the driver tube is also one of these non-standard pinout tubes.


Posts on other forums where I posed this question would agree with you. I'm still fairly new to tubes, and I'd never heard of the 7591 until this morning. After looking up the tube spec sheet and studying the pinout, I agree that its likely what this chassis used. Those threads are at https://audiokarma.org/forums/index.php?...s.1032663/ and https://el34world.com/Forum/index.php?to....msg335329 for referense.
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