Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ampnewbie on October 15, 2021, 09:02:34 pm

Title: 6420 tone control buzzy?
Post by: ampnewbie on October 15, 2021, 09:02:34 pm

Hi everyone, I have built a clone of the supro 6420. Schematic that I used is here: https://el34world.com/charts/Schematics/files/Supro/Supro_6420ss_tbolt.pdf

It works great but one thing is weird. As I turn the tone control up between 1 and 4 o’clock I get a buzzy noise that goes up around 1 and is gone around 4 or so. After that there is no noise all the way up to max.

Any ideas? Would it help if I used the unused triode as a cathode follower to help drive a stronger signal to the tone control?

Thanks!

Title: Re: 6420 tone control buzzy?
Post by: PRR on October 15, 2021, 10:03:26 pm

> between 1 and 4 o’clock I get a buzzy

That's where the wiper impedance is highest. Most susceptable to any buzz in the area. Where does the wire off the wiper go past?

Title: Re: 6420 tone control buzzy?
Post by: ampnewbie on October 15, 2021, 10:12:26 pm

Ok, yeah, it crosses a few other wires. I just moved it close against the back of the pot as much as possible and that made it less noisy. I may try shielding it tomorrow. Thank you.