Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: sjwood3 on April 18, 2020, 12:02:43 pm
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I'm new here and looking for suggestions. Main question is what Classic Fender amp that fits the chassis would you create?...I have a 1972 Quad Reverb chassis. It came with most of the pots, knobs, switches, Schumacher power transformer (J022756), choke, and reverb driver….and that’s it. I've stripped it down and cleaned up all the sockets, pots, switches, and the chassis. So to me it looks like a great canvas for a kit. I’m not an engineer, but I’d love to get this thing back to life. I have a head cab that it’ll live in once done as well. Can you make a suggestion for which amp I should go after? I’ve considered the Silverface era early 70s Twin Reverb with Master volume. The particular transformer specs I found on Dougs Site were: 022756 (120v, 345-0-345, 310ma, 6.3v/6a). From what I can find that power tranny was quite common in the twin reverbs from that era as well. Let me know if you have any immediate or slowly evolving thoughts! Thanks for your time.
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Super Reverb or Deluxe Reverb, both AB763 circuit.
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Well, a twin reverb would fit that chassis perfectly, and match up with that PT. Hoffman has a board for his AB763 amp that would work well. Or you could also use his twin reverb board.
The quad and the twin are basically the same amp, just different OT and speakers.
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Great project. I got a 73 Quad Reverb (complete) chassis the year before last and put it into a low profile head cab (with a little bit of work). Run it with a 75 DSR Cab - makes the bels really sing
As for the type of amp, the Quad, Twin, SuperSix and Dual Showman Reverbs of the same era are identical except for the speaker configurations (The Vibrosonic Reverb is nearly identical but has a different OT and single speaker)
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Schematic FYI
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Great project. I got a 73 Quad Reverb (complete) chassis the year before last and put it into a low profile head cab (with a little bit of work). Run it with a 75 DSR Cab - makes the bels really sing
As for the type of amp, the Quad, Twin, SuperSix and Dual Showman Reverbs of the same era are identical except for the speaker configurations (The Vibrosonic Reverb is nearly identical but has a different OT and single speaker)
Yes! Thats the exact low profile cab I have as well. Any problems with reverb hum because of the tank proximity to the transformers?
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Great project. I got a 73 Quad Reverb (complete) chassis the year before last and put it into a low profile head cab (with a little bit of work). Run it with a 75 DSR Cab - makes the bels really sing
As for the type of amp, the Quad, Twin, SuperSix and Dual Showman Reverbs of the same era are identical except for the speaker configurations (The Vibrosonic Reverb is nearly identical but has a different OT and single speaker)
Yes! Thats the exact low profile cab I have as well. Any problems with reverb hum because of the tank proximity to the transformers?
None. (You need to keep the output transducer end of the pan away from the PT end of the cab)
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Great project. I got a 73 Quad Reverb (complete) chassis the year before last and put it into a low profile head cab (with a little bit of work). Run it with a 75 DSR Cab - makes the bels really sing
As for the type of amp, the Quad, Twin, SuperSix and Dual Showman Reverbs of the same era are identical except for the speaker configurations (The Vibrosonic Reverb is nearly identical but has a different OT and single speaker)
Yes! Thats the exact low profile cab I have as well. Any problems with reverb hum because of the tank proximity to the transformers?
None. (You need to keep the output transducer end of the pan away from the PT end of the cab)
Glad to confirm that info. I've read it several places, and was a little worried about hum while cramming a Twin Reverb into a small space with a reverb tank.
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I put this Twin into a Bassman 100 cab, no problem.
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Ordered the parts for a Twin. Should be a fun one!
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What am I missing? If you have the power transformer don't you need the output Transformer. I just had one of my dizzy spells a little earlier so am I really losing it. I am being sincere.
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Yes I only initially had the PT. I have since ordered and installed an output.
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Hey, I've been working on one of those too!
A previous owner converted it to AB763 specs, or tried. Once the existing wiring errors, plus my own :icon_biggrin: were fixed it sounds great. More than loud enough for me!
The empty Master Volume position bugged me and I thought it might be nice to have, so I added a master volume. "Trainwreck type 2/Lar-Mar" https://robrobinette.com/AB763_Modifications.htm#Master_Volume_Mod_
That appealed to me because at full volume, it's electrically the same as the AB763 without MV so it lets me get the full "original sound" if I crank it all the way up. And it's really nice to have the MV because I get to play with at least some sort of overdrive tone on this amp, and I would simply never have the opportunity to do that without it. Well, maybe if I get a good attenuator in the future.
Note that if the pot goes bad, this one is much less safe for the tubes than some other designs however... I knowingly took that risk but you might not choose to.
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I'd lovee to see a picture of the innards if you snapped one. Mu idea was to do the Frondelli Master Volume. RobRob says,
"The Frondelli is my favorite master volume for several reasons"
Plus its safer for the tubes if the pot fails. I like the push/pull option as well. Still a theory. I have to get the amp running first!