Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Diverted on April 10, 2024, 09:19:38 pm
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Hi all,
I just finished wiring up the circuit shown below, only changes are I removed the choke (100 ohm resistor), went with diodes for rectifcation and added a negative feedback on/off switch and a 100K mid/raw pot. There is a thermistor in the hot AC line.
The amp sounds fantastic and super quiet at idle except for a quiet but noticeable buzz from maybe 2 to 4 oclock on the volume knob. After that it quiets down again.
I'm wondering how to eliminate or lessen this. My wiring is pretty tight and not easy to adjust, apart from the tone stack wiring out of the preamp. Would I be better off running the three wires from the 250pf, .047 and .1 separately, as opposed to twisted as seen in pix?
Any other suggestions on how to root this out? I would love a clean sweep of the pot. Thanks.
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Leo liked to twist the tone stack wires. See the blue, brown, and white twisted wires in the pic.
Just spitballing here... Try connecting a 1M resistor between the volume pot wiper and ground. Or replace the pot. Is that the power switch on the back of the volume pot? Yuck. Disconnect the switch wires and move them far away from the volume pot and temporarily solder the wires together. Any better?
(https://sluckeyamps.com/64DR/06.jpg)
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Try adding a grid stopper at lug 5 of the 6V6, value somewhere in the range 1k to 22k.
Does the issue occur with nothing plugged into the inputs?
If yes, how about if the input grid lug is grounded?
I think the wiring to the fuseholder is going to the wrong lugs, live should be the back lug, not the side.
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Thanks for the suggestions.
Yeah I agree with the switch on the pot… I’d rather not but my friend wanted it. If relocating it kills the buzz I’m over-ruling him. I will also try the 1M, and grid stopper. Thank you.
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My buddy is getting overruled. That crappy Alpha on/off switch on the volume pot was the culprit. Oh well. I ran the pots lug down and AC line high up above hoping that would keep the noise away, but I guess not to be. A standard switch it is. While I was at it I added a 1.5K grid stopper for the heck of it. Thanks all.