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I have a 1958 or 59 RCA Victor stereo amp, which does have a mono selection. It runs on 5Y3, 6CG7 (3), and 6V6GT (2). It currently red-plates the 5Y3, but other than caps, I think it's good. What I'd like to do is make a high gain guitar amp out of it. I'm thinking my best bet would be to keep the 6CGC7's and use the 6V6's in push-pull, which would only require a different output tranny, and use half of a 6CG7 as a phase inverter. Any experts out there know if this would work and if there is some similar design amp out there?
R.W.R.
Follow Ups:
The OEM power transformer has a 2 A. 5 VAC winding, for the 5Y3. Switching to a 5AR4 increases the B+ rail voltage and allows for a larger valued 1st filter capacitor, without increasing the demand on the 5 VAC winding.
Don't go "hog wild" in increasing the amount of capacitance in the 1st filter position.
This Edcor model should be fine for a PP 6V6 guitar amp's O/P "iron".
Eli D.
My suggestion would be to replace all three 6CG7s with 12AX7s or 6N2P (Russian "6AX7"). The first 'AX7 would serve as one or two gain stages for the guitar input. The second would be a grounded cathode gain stage direct coupled to a cathode follower to drive TMB tone controls. The last 'AX7 would serve as a LTP phase inverter. This is a common topology used in many Marshall and Fender amps.
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Buy Chinese. Bury freedom.
Lots of good info here on the Marshall Plexi and Master Volume designs. Much of this is applicable to Fender, too. This article was a big factor in deciding to build my own Marshall-esque amplifier. I essentially took the 2104/4010 MV design and added reverb and a buffered effects loop.
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Buy Chinese. Bury freedom.
Thanks Triode Kingdom, I really like the cold clipper circuit. I am no experienced amp maker, so it's a little complex. I don't have a center tap on my 6.3v filament supply, but I guess there is a way around that, for the 12X7's. Also don't know what difference my tube type rectification would have, if any. Gonna study this Marshall stuff closer and give it a try if I feel I can follow the given's and convert it all to a lower power. I don't think Two 6V6's in push pull could deliver anywhere near 50 watts, so...
R.W.R.
"I don't have a center tap on my 6.3v filament supply, but I guess there is a way around that, for the 12X7's."
Same here. I used two 100 ohm resistors from each side of the winding to create an artificial center tap. Rather than grounding them, I applied about +75V (voltage divider from B+) to help prevent hum.
"Also don't know what difference my tube type rectification would have, if any."
I added a separate 5V filament transformer to mine and used a 5AR4. Your 5Y3 will work just fine. SS diodes are one thing I don't like about the Marshall design.
"I don't think Two 6V6's in push pull could deliver anywhere near 50 watts"
A pair of 6BQ5s is typically used to create what's known as an 18 watt amplifier. 6V6s fall into the same category, although in fact they output a few watts less. There are schematics scattered around the 'Net showing many Marshall-type builds using both tube types.
Good luck!
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Buy Chinese. Bury freedom.
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