Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Pavels07 on September 13, 2022, 10:32:03 am
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Hello all,
I've been wrestling with a V1 Hot Rod Deville 212 for a bit (complete overhaul of caps, rebuilt the Low Power resistor section that always burns out) but was still experiencing a Thunderstorm style crackle and noise even after thoroughly cleaning tube sockets and replacing tubes. It didn't change plugging directly into the effects return and was not effected by the master volume knob either. Doing some tests outlined on the GeoFx page, I found a shorted winding on the output transformer. I ordered a Hammond 1750L (as suggested by Hammond themselves). After installing and excluding the Ext. Speaker Jack (customer never uses) I am experiencing a loud hum which I have pinned down as coming from the Grey Wire responsible for the Presence Control/NFB (schematic will be attached below). Disconnecting this wire eliminates the hum, but at the sacrifice of the Presence control working. Is there something I am missing? Is this one of the scenarios like the Bassman AB165 -> AA864 conversion where the wires should be switched? I am open to ideas and suggestions.
Thanks!
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Verify the OT black wire connects to ground. Swap the OT blue and brown wires. One or both of these should fix the problem.
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Yes very common, especially on new amp builds. You have a 50/50 chance of getting the wiring right. If there's noise swap the OT leads as suggested. Usually fixes it.
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Swapping the Brown and Blue Primaries did it. Feeling really dumb about not thinking about that.
Thanks for coming through as always Sluckey and JPK!