Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Carlsoti on August 21, 2022, 01:15:08 pm
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Here's an interesting beast. Choir-Tone, likely a custom build from the early to mid 70's.
Looks like a 4-channel, all-tube mixer with reverb, T/B tone, and volume control for each channel. Tube compliment is 5ea- 7025, 2ea-12AT7, 2ea-6550. It's got a solid-state rectifier and MASSIVE iron.
Does anyone know who may have manufactured the transformers with the part numbers PX3430, PX3431, PX3432, and PX3433?
FWIW, the pots seem to be CTS units that date to around mid 1971.
Any insight you could provide would be greatly appreciated. Thanks.
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> who may have manufactured the transformers
https://img1.wsimg.com/blobby/go/2bc5e4f5-4ae0-4244-b91d-fbafeabfb639/downloads/13%20Transformer%20EIA%20codes.pdf
https://el34world.com/Forum/index.php?topic=27470.0
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I guess I'll pull them and see if I can find the data stamped on it somewheres. Thanks.
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I pulled the chassis again, but can't find any stampings on the outside of the transformers. I did find out that this is likely a re-painted AIMS amp, out of Arizona. I'm certain to do something with this, but what exactly, I'm not sure yet. I think I'll need to see what kind of voltages I've got in it before making any decisions. 6550s are not inexpensive these days. If I can sub in something cheaper, I probably will.
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Investigate about OT spec, post It and maybe we can find a sub for the Power tube
Franco
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6550s are not inexpensive these days. If I can sub in something cheaper, I probably will.
if you produce almost the same amount of power as a quad of el34 or 6l6 are a pair of 6550 (I'd rather get 6550a or kt88) so expensive?
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@kagliostro - Thanks. Being an octal, there's got to be at least one simple swap, given appropriate bias adjustment. I have a feeling that these amps, in good working order, have something north of 500V on the B+. I think we can scratch 6V6s off the list. lol.
@thetragichero - Great point. $/W, 6550s aren't THAT ridiculous, but given that I don't play live and have shared-walls with neighbors, I can give up output wattage in exchange for $$$ savings.
I've got a bunch of other stuff that needs to be worked on for others, so that pile takes precedence. I'll come back with more info when I have it.
Thanks y'all!
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> I don't play live and have shared-walls with neighbors, I can give up output wattage in exchange for $$$ savings.
Tubes are just valves. The power supply here seems to be 620 Volts. Smaller tubes will just die.
Agree this is a re-painted (why??) "something" and AMS is likely. We did a round on this amp but different input provisions a decade ago. When some of use were "codgers". (I like to think we have grown out of that phase.)
https://el34world.com/Forum/index.php?topic=14405.0
There's a PDF schematic down-thread.
The input stage is, uh, unique (50V??). Most of the rest is cribbed from the Fender playbook (I read that AMS was Fender people). The killer detail is running 610V on the screens. Insane, Not legal even on EL34. Or 6550. >500V on G2 not needed even on huge transmitter tubes. These boys didn't read the book.
And BTW: it is said that AMS offered a "Lifetime warranty".
Good write-up elsewhere:
https://gearspace.com/board/so-many-guitars-so-little-time/871577-1970s-aims-vtg-105-guitar-amp.html