Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 87MJ on June 03, 2011, 10:31:12 pm
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So I built the AB763 DR as a first build about 3 months ago, but with a tweedish normal channel mod that I found somewhere online, and reverb both channels. The rest of the amp is the Hoffman circuit (with bias tremolo). Really I had no idea what I was doing when I laid it all out other than what I read online.
Anyway now I'm looking to tweak the tweed channel (since I can...). It sounds pretty good as is, with a straight up old school distortion, but it gets blatty on the low notes with the gain turned up, also its maybe a bit too edgy overall. The gain is there that I like, but I'm looking to smooth it out, and get rid of the blat.
So far I've just done things that can be alligator clipped on (no desoldering yet). I've played around with parallelling the plate resistor with a variety of caps on V1A/B, also parallelled a 680R on the cathode resistor on V1A (467R effective), and like how that turned out.
So what would you do next? I'm looking for some suggestions how to tweak this preamp. I'm thinking of swapping V1B plate resistor with a 220k and 2.2k on the cathode to bias it the other way? maybe something else?
Partial schematic attached - the rest is Hoffman AB763.
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> it gets blatty on the low notes
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Thanks PPR, I will try that next.
Also I forgot to say in my OP - I added a B+ node for V1 that provides B+ of 215V.