Sorry to be so frantic here!
Finally figured out that it was a nasty ground loop.
On this amp the PCB is about half visible through removable...
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Measured 0VDC on both V1A and V1B grids....Last edited by hylaphone; 03-02-2024, 10:16 PM. Reason: Rechecked this after stepping away for a bit, was mistaken about that DC path from V1 Cathode... obviously that lands after the second coupling cap.
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Yes original PT, and I actually tested that by trying a humdinger pot instead of the CT. No change in the buzz...
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Just threw a new one in, no change --
Also, the Sharp/Deep circuitry seems ok, they function correctly and I checked continuity between all the...
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Correct, grounding 1st grid just makes louder hum.
I pulled the 1st anode resistor and the hum disappeared...
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I was mistaken, it's mostly 60Hz --
I did swap V1 to no avail....
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Univox amp Buzzz
Hi gang, I have a Univox 1236 here with a wild amount of 120Hz buzz happening in the 1st stage. It disappears when the 2nd grid is grounded. I've exhausted...
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Great, I'll chew on that for a while. Thanks again!...
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I don't understand, how does parallel R45 change the source resistance? Not sure what is happening earlier in the Rockman, but mine will be driven by Mosfet...
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Cool, thanks. So, R44 and R45 knock down the signal, and R44 C34 low pass at 150Hz? How does the impedance ratio figure in?...
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Sorry guys, I should have clarified. This is for bass guitar, dude just wants to knock off the highs coming through the monitors.
I think an RC or LC...
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hmm I hadn't thought of that. Don't have a full schem drawn up but basically after the second triode the signal splits to two volume controls, each feeding...
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Thanks for the suggestions. I thought of bypassing the plate resistor but am iffy about having B+ at the switch. Here is the schematic, just the Bass Instrument...
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LPF placement
Hi folks, I have BF Fender style preamp here and the customer wants a switchable LPF around 4kHz. What is the best approach to add a simple passive filter?...
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Well, I re-flowed a few of the B+ joints on the PCB, and the amp is nice and quiet now. *Slightly* disappointed I couldn't find the specific culprit, but...
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Yes I have, and replaced the standby switch as well.
If what you suggest is the case, I'm not sure how to troubleshoot it from here....
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Yes, and the popping persists. This also rules out R4, etc. This amp must be a later one, the resistors are all carbon film....
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Ampeg Portaflex POPS
Hi folks, I have a 70's SB-12 on the bench with constant popping sound. It is volume dependent, suggesting an issue in the first half of V1. It occurs every...
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