Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hiegdk on February 11, 2024, 04:32:12 pm
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Hi all, I'm taking a look at a garnet Pro 200 that a buddy of mine recently bought. It's had recap at some point and the person who did it mounted radial caps to new tag boards inside the chassis - which seems fine. I was noticing some oddness though so I traced the modified power section wiring (see attached schematic). It seems like the lamp was rewired to draw power from the final filter stage (E) rather than immediately after the rectifier (A) as in the original. Is this a potential issue that I should correct, or is it ok to leave it? The odd behaviour this seems to be creating is that the lamp doesn't turn on when the amp is powered up. Once the amp is taken out of standby the lamp turns on, which make sense given the new wiring. The lamp also stays lit for at least 30 seconds after powering the amp off.
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All normal. If you want the lamp to be on regardless of STBY switch position, then move it back to Node A.
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Don't forget the links E-caps to junctions of 220k for correct cap voltage sharing.
Regards
Mirek
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Thanks slukey - that's what I figured but thought I'd check. I haven't encountered an amp that didn't use either the mains or the heater supply for the lamp - using the rectified HT like this seems like an odd choice.
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Don't forget the links E-caps to junctions of 220k for correct cap voltage sharing.
Regards
Mirek
Yeah, I just missed those when jotting down the wiring - they are joined like that in the amp. Thanks!
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Ok, new question. I'm seeing something in the "Stinger" section I'm not understanding. There appears to be a 10M resistor connecting the "Stinger" footswitch jack's tip to the Bias supply. What would this be doing? Some sort of phantom power for an indicator in the footswitch (I don't have the original footswitch for this amp, if it came with one). The schematic is here: https://el34world.com/charts/Schematics/files/Garnet/Garnet_lb200f_pro200.pdf
Photo for reference attached.
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Impossible to guess from the photo and there is no 10M connected to the footswitch in the schematic you posted.
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Impossible to guess from the photo and there is no 10M connected to the footswitch in the schematic you posted.
Yeah, it doesn't look stock (CF resistor rather than CC). Hard to say. There's something sort of like that in the standalone Stinger schematic in the library, but I'm not familiar enough with it to know what's going on.