Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: munkeyboy on November 21, 2019, 11:28:14 am
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I've had two projects in the past two weeks dealing with Japanese 3w-5w amps. One was for a client who wanted his Teisco 71R fixed and another where I converted a Truetone (western auto) reel-to-reel to a Gibson GA-5 circuit. Both amps have quite the small and probably cheap OTs and both had a slight fizz on higher gain notes. It could just be the character of these amps, but wondering if it could be transformer ring and if a snubber circuit (corrective filter) would possibly help. How would that look on a SE amp?
Related note, the Truetone did have a 1M resistor across OT primaries. I think that is part of a snubber circuit right? But there was no other cap with it.
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both had a slight fizz on higher gain notes
are you sure it's not coming from the preamp section?
most small watt SE have enough pre-drive to overdrive the PA by twice.
if you don't have a scope or listening amp you can kinds/sorta get an idea by
"un-bypassing" the PA tubes cathode. That knocks out some gain. You can do the same in the pre.
I've never used a snubber in the PA, have in the PS
slight fizz on higher gain note
since it's on both probably not parts, but if you did use old n mold R's for plate Rs they can give you some fiz/hiss
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both had a slight fizz on higher gain notes
are you sure it's not coming from the preamp section?
most small watt SE have enough pre-drive to overdrive the PA by twice.
if you don't have a scope or listening amp you can kinds/sorta get an idea by
"un-bypassing" the PA tubes cathode. That knocks out some gain. You can do the same in the pre.
I've never used a snubber in the PA, have in the PS
Never used a snubber period, so not sure where it goes :D I thought it was supposed to hang off the output transformer.
slight fizz on higher gain note
since it's on both probably not parts, but if you did use old n mold R's for plate Rs they can give you some fiz/hiss
On the Teisco for the client, I didn't replace any Rs, just caps. So that is a possibility tho I know that bad R crackle sound and this is different than I've heard. I have since handed it back to him. I told him I wasn't happy with it, but he seems to like it or at least doesn't want to spend more on it :dontknow:
On the Truetone, it is a completely new build, only reusing iron and chassis. Either amp isn't really that bad, (not like that danelectro i'm working on) and I'm probably just being picky as they still sound good. Especially the new build. But I'd be curious to know more about what a SE snubber would look like and just try it for fun.
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just try it for fun.
try something like "snubber circuits in audio amplifiers" that should get you at least 2 pages of folks willing to sell you one, :think1: valid data :dontknow:
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Ha
Well Shooter I might be wrong. Just listening to this truetone again... Does kinda sound like a bad resistor or more likely a cold solder joint since everything is new :BangHead:
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Nope, like my danelectro, poor voltage on preamp plates. Bonehead move, didn't look at PT voltage when converting to champ circuit. Too much filtering. Dropped the R from 22k to 1.5k on the last filter cap and now I'm good.