Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TWANG on September 24, 2021, 04:00:16 pm
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I have changed preamp tubes, twice.
The 6V6s are new (EH).
I found the 270Ohm 10R read 0.L when tested.. chopsticking showed me noise off
that R so I replaced it.
That reduced some ground noise I was hearing (esp. when I turn guitar vol. down) to nothing.
Amp sounds great. I have three 5E3s here that I built. (PPWATT 5E3 board)
I have ordered a new JJ rectifier tube. The one I'm using is an Old RCA.. god knows where it came from.
I think I will lift the board up so I can see the bottom, since I've tested voltages and they are ok, and I only found the one chopstick problem.
(I hate doing that when everything is wired in.)
But these are ugly noises, not all all anything you might get from really driving an amp like this. And sometimes I do.
Like there's a short and someone is moving the wire about..
All good stuff though, Classic Tone OT's et al.
I've been over Robinettes site and others and I've certainly done all the testing, save what I mention above.
Something else is bad though.. no doubt about that!
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Sounds like plate resistor, pull the pre tube out, still there? Check phase resistors. Just a thought.
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Sizzling bacon.
I have same sound from a amp I fix. It was bad solders I do, new lead free solder need more heat.
Tubes rectifier are easy to check ; read DC voltage at the output. Don't order one if you don't need it
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Maybe a cold solder joint. That sounds like that too...
It's very important the components are well mechanically connected before soldering. When you add solder around a looser wire or connection there can be a bad transfer of current. Don't say it's the problem, but just in case.
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I went in there with a vengeance.
Mostly because I had 'fixed' this amp three times, which meant total assembly disassembly. argh!
I decided to swap out a few components that were in kinda sloppy.
(and used some better ones.)
then I found a HUGE blunder.. on top of a few solder joints that were very questionable.
turns out, there's a big difference between 100 Ohms and 100 THOUSAND Ohms.
Especially in two places.
(You know where!!!)
I felt such an idiot.. all that looking and right under my nose.
big mystery, eh Twang?
I don't know how I have enough guts to tell you all. :dontknow: :sad2:
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Strengthens your character... :thumbsup: