Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: shaun on June 01, 2020, 06:20:32 pm

Title: Stereo Champ?
Post by: shaun on June 01, 2020, 06:20:32 pm
Heyo,
I have a gutted RCA Victor hifi stereo. I've got the PT and 2x OT still in the chassis. No schematic available after searching the chassis number etc, and no model number available, but it was running a single 6V6GT per side for power tubes. I'm going to try to turn it into a Champ stereo project.

After extensive researching online and elsewhere, I haven't found anything that explains (to an amateur) how two amps interact in the same chassis, but I'm sure there are practices that need to be taken into account. For example, in the chassis, the RCA OTs were wired out of phase to each other on the primary side, which I'm guessing was a hum cancelling strategy. Or a wiring error that was corrected by switching speaker leads on one speaker later on. But assuming it wasn't a mistake, I'm wondering the reason behind having the OTs out of phase in an SE stereo amp.

As always, thank you to those so much wiser than myself in these matters.
Title: Re: Stereo Champ?
Post by: Toxophilite on June 02, 2020, 07:41:25 pm
I made a kind of stereo vibro champ built using a roberts reel to reel chassis etc. Shared power supply. Worked fine. Didn't do anything other than the original did. The preamps for the two different amps share a 12ax7 and I used an ampeg stereo echo twin output transformer driven 'stereo reverb' too. Go for it.
Title: Re: Stereo Champ?
Post by: terminalgs on June 03, 2020, 09:53:45 am


Look at stereo amps from the 60s:   

Valco (and Airline, National, maybe Penncrest) didn't advertise it as a stereo amp but I include it only because it does have twin outputs and it might be an idea for your build.  It was Valco's way to make a 70W amp without sourcing different OTs (2 35W power amps sharing a single PI). 

If you want two different tone stacks, the GA78RV and the M15 are good ones to study.  If you want a single tone stack, check out the Valco.
Title: Re: Stereo Champ?
Post by: SILVERGUN on June 03, 2020, 10:03:39 am
Quote from: terminalgs on June 03, 2020, 09:53:45 am

If you want two different tone stacks...
Just my .02
Maybe just one tweed champ and one blackface and blend the tones with the volume controls.  I would think that the tweed side would inherently be louder with all else being equal.
Title: Re: Stereo Champ?
Post by: shaun on June 03, 2020, 12:26:06 pm
Thanks guys. Much appreciated. I'll check out those schematics. Good food for thought.