Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Zarrir on September 09, 2016, 02:10:02 pm
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Hi! Just finished a Hoffman Stout 18 watt Marshall Clone. Turned it on and it plays fine. However, there is this high pitch squeal which is present even when the volume and tone knobs are all the way down and the guitar cord is unplugged. All tubes are new, and no microphonics are present on them. I am using a JJ 40-20-20 can cap . Input jack has only two tabs, seems to be properly grounded to the chassis through its washer. I have no shielded cable from the input jack to the first tube because the input resistor is connected directly between them. Stains on the chassis are from the anti rust treatment, no bugs. Any ideas?
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Overview
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swap position of the OT primary leads.
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> even when the volume and tone knobs are all the way down
Probably not the input jacks. I would chopstick the OT and pot leads to see if it changes.
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After you swap the OT plate leads maybe you could fix the preamp end of the board. Just move the top lead of those components to the right. Move the jumper too. Then you can put that dangling cathode resistor/cap on the board like the layout shows.
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Thank you guys. So i will swap the blue with the brown leads. Gosh Sluckey, this is what one extra beer does to a guy. I thought i had run out of turrets and simply let the cathode resistor flying over.... :BangHead: Will post results.
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UPDATE: Thank you guys! That did the trick!! Swapping the OT primary leads killed the whistle. Sluckey, should i keep the cathode resistor flying over like some kind of "mojo"? :laugh:
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That would definitely be a kind of mojo. I'll let you make that call. :wink: