My Hoffman Twin Reverb - FIXED - Whats next?

[proaudioguy]

For those following at home.


I really appreciate all the help here.


I lost one of the PSU series caps.  I ordered new ones, from a different dealer because I also needed some other stuff that I had to get there.  One of the TADs I put in about 10 years ago (amp hasn’t been used much) went OPEN.


So I put the new caps in and I just did all 5 of them.  I used F&Ts this time.  I almost just bought the spragues, but I know a lot of people like F&Ts.


I had also lost 4 of the 6 diodes in the rectifier but the 2 left were doing the job.  In anycase I pulled all the 3A diodes out which was more difficult than it was to install them, and I replaced them with IN4007s which were a lot easier to install, although I supposed if I lose 1, I lose all 3 on that side, so there is a trade off.


So then back to the reverb driver tube freak out problem that was causing this horrendous distortion.  I went back and checked all my voltages.  Most of them were up compared to before that first cap dying so possible the cap was already dying.  I tried several possible fixes some of which included mutilating the 500pF cap between the plate on V2B and V3 Grid so I replaced that cap.  Then I stuck a 120pF between the plate and cathode on V3 and that solved it!  I had tried all sorts of lead dress with no luck.  It has to be a layout issue with the board.  To be totally clear, though, DOUG didn’t make this board and the guy that did, definitely didn’t lay it out exactly the same as Doug either.  Its entirely plausible this problem was created in the layout but I am not experienced enough to know.


I biased it to just under 70% which totally killed the tremolo.  I had noticed even with the tremolo sounding great at low volume, which cranked all the depth went away anyway so I biased it for tone.  Now I need to work on getting that so it works.  Now, I might go with Sluckey’s circuit and just install a switched pot so the pot can be removed from the tone sucking position of sending signal to ground even if the tremolo is OFF.  What about using Sluckey’s tremo, but keeping the large pot?  What is the ramification of that?


What else?  What should I do to the Normal channel?  If I mod to Marshall tone stack will that get me close to Marshall, or something good, or are the EL34s too much of that recipe to overcome?


Any other mods I should do?

[proaudioguy]

One more thing.  No one ever answered me about if the drivers on the 6G16 tremolo amps move in and out even when the tremolo was OFF.  I asked here several times and I also posted on several other forums and never got an answer.  In fact I still don’t have an answer.  What I do know though, is once I replaced all the PSU caps, that was reduced dramatically and even with the bias set really hot, like -50V where the tremolo was the deepest, they only moved slightly when the tremolo was ON and intensity was at 10.


SO THE ANSWER APPEARS TO BE NO, they shouldn’t be moving.