Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Dimitree on October 24, 2020, 05:25:14 pm
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so after building a Vox AC30, a Fender Princeton Reverb and a Fender 5E3, I really want to start building a Super Reverb.
But it won't be a standard Super Reverb, instead I'd like it to be stereo.
What I mean is having two separate audio amps in the same chassis/cabinet, each one driving a pair of 10" speakers (as you know the Super Reverb is 4x10").
Reason for this is that I'd like to use stereo effects (particularly chorus) and mimic what the Roland JC120 does (dry signal on one speaker, wet signal on the other speaker).
I will remove the normal channel and tremolo circuitry, but keep the reverb.
Then I will need to duplicate the whole audio path (except reverb), and add a second output transformer.
I guess I can keep a single power transformer, provided that I add an additional 2A or 3A filament transformer to supply the new tubes.
Also, a single GZ34 won't supply enough current for 4x 6L6. Two GZ34 in parallel is asking for troubles (if I'm not wrong), so I'd say I need to use a WZ68 Copper Cap (Equivalent of 2x GZ34, 450mA).
Would those mods be enough to keep the single 125P5D transformer? or maybe I just need a Twin Reverb transformer.
I will use dual gang potentiometers to control both circuits at the same time. Initially I thought about using a single preamp, and adding a (mono)send/(stereo)return after the preamp, but I guess it would be easier with dual potentiometers.
I will make it switchable so that I'm not forced to feed a stereo signal to use all of 4 speakers.
what do you think? can this be done?
I have some questions:
1) how the output power of the amp will be affected using a pair of power amp driving 2 speakers each, instead of a single power amp driving 4 speakers, keeping the same output impedance?
2) what should I do with the reverb? I guess the simplest way would be to keep the reverb on one channel only, remove the existing mix potentiometer (wired as attenuator) and use a dual potentiometer wired as crossfader to get 100% wet on that channel
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My suggestion would be to use a 100 watt power transformer such as the Twin Reverb or Dual Showman PT, and then use 2 of the 50 watt output transformers. Personally, I would use a solid state rectifier, but if you want to use a tube rectifier, go with your idea of the WZ68. Although, the Fender 5F8-A Twin amp used a single GZ34 with 4 5881s...
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... Super Reverb ... I'd like it to be stereo.
... two separate audio amps in the same chassis/cabinet, each one driving a pair of 10" speakers ...
On another forum, folks gripe about the weight of their amps. A group of folks on that forum say the Super Reverb is one of Fender's best amps; another group opines the reason blackface Super Reverb amps are cheap compared to the Princeton Reverb & Deluxe Reverb is that their weight (65lbs according to Fender (https://shop.fender.com/en-US/guitar-amplifiers/vintage-pro-tube/65-super-reverb/0217600000.html)).
Whenever someone brings up building 2 amps in 1 box, the weight issue has to be raised.
... two separate audio amps in the same chassis/cabinet, each one driving a pair of 10" speakers ...
... enough current for 4x 6L6. ...
Would those mods be enough to keep the single 125P5D transformer? or maybe I just need a Twin Reverb transformer. ...
You can't power 4x 6L6GCs from a Super Reverb power transformer; you'll have to use a Twin Reverb PT (like Hammond's 11.65lb 290FX (https://www.hammfg.com/electronics/transformers/guitar/twin-reverb)). Part of the "Super Reverb sound" is the big output transformer (like Hammond's 4lb 1760K (https://www.hammfg.com/electronics/transformers/guitar/super)).
You're up to ~20lbs and don't have anything else that makes up the amp. Based on Fender's weight for the Super Reverb, expect your amp to weigh at least 73lbs (heavier than a Twin Reverb (https://shop.fender.com/en-US/guitar-amplifiers/vintage-pro-tube/65-twin-reverb/0217300000.html)).
... Reason for this is that I'd like to use stereo effects (particularly chorus) ...
Why not use 2 small amps instead, either in a Left/Right setup, or a Wet/Dry setup? What advantage do you obtain from putting it "all in one box"?
https://www.youtube.com/watch?v=LIjgOC_PLYM&feature=youtu.be&t=86 (https://www.youtube.com/watch?v=LIjgOC_PLYM&feature=youtu.be&t=86)
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My suggestion would be to use a 100 watt power transformer such as the Twin Reverb or Dual Showman PT, and then use 2 of the 50 watt output transformers. Personally, I would use a solid state rectifier, but if you want to use a tube rectifier, go with your idea of the WZ68. Although, the Fender 5F8-A Twin amp used a single GZ34 with 4 5881s...
I built a stereo power amp on the forum here somewhere, based on a Sunn Dynaco, power amp section. I used a 100 watt PT from a Carvin MTS 3200. Works great. Train-wreck OT- But no Ultra linear. A 100 watt PT with 4-5 amps filament would be great to include the preamp stage.
... Super Reverb ... I'd like it to be stereo.
... two separate audio amps in the same chassis/cabinet, each one driving a pair of 10" speakers ...
On another forum, folks gripe about the weight of their amps. A group of folks on that forum say the Super Reverb is one of Fender's best amps; another group opines the reason blackface Super Reverb amps are cheap compared to the Princeton Reverb & Deluxe Reverb is that their weight (65lbs according to Fender (https://shop.fender.com/en-US/guitar-amplifiers/vintage-pro-tube/65-super-reverb/0217600000.html)).
Whenever someone brings up building 2 amps in 1 box, the weight issue has to be raised.
The amp I built weighs quite a bit. 3 transformers and a choke, chassis; blah blah; two 12 big metal speakers cabinet. I recently loaned it out unsolicited to a friend as I know he'll take good care of it. Personally, now, if I play at all, I run thru powered speakers and a modeler. And yeah, "who plays out?"
Great learning experience though.