Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on December 07, 2014, 02:30:29 am
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Hi guys, I've got the main PCB out and a complete rebuild will be done.
The tropical fish caps replaced with 630v polypropylene.
CF resistors replaced with .7w metal film.
2w CF resistors replaced with 3w metal oxide.
Ecaps replaced with F&T 22uf/500v.
Both 100uf/350v cap cans will be replaced with JJ50+50/500v cap cans.
The rectifier diodes look fine, so do these need to be replaced??
Same with the bias diode??
It has a 50v bias tap and the fixed bias was set at -54v, this seems a bit high????
With the layout of the PCB it looks easy for a FENDER type adjustable fixed bias.
Which of the resistors will determine the "RANGE"
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fwiw I just did a couple repairs that had 2 of 4 bridge diodes blown, n both amps, sometime in the past someone had replaced the other 2 so for a couple bucks, maybe?
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I would replace the 680Ω with 1500Ω and replace the 8.2K with a 10K trim pot in series with a 10K resistor. Wire the pot as a rheostat, ie, connect the wiper to one of the outer legs so there are only two connections to the pot (Marshall style).
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Thanks Sluckey, Just trying to picture it fitting into the PCB with the traces the way they are. :think1:
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Thanks Sluckey, Just trying to picture it fitting into the PCB with the traces the way they are. :think1:
You could use a Fender style chassis mounted 10K pot with the 10K resistor mounted directly on the pot. Then just run a single wire to the pcb. Very clean and easy.
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Thanks Sluckey,sorted.