Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Stuff4bikes on June 13, 2021, 11:09:08 pm

Title: Ugh.......been here a while but first post. Champ circuit.
Post by: Stuff4bikes on June 13, 2021, 11:09:08 pm

Followed the robinette champ to a T, except using 6F6GT and 5Y4GT. I have done several champs/princeton's before with only minor issues but this one is thrown together with used parts and giving me fits.
Oh 500k volume pot, so that's a change also.

If I ground the lug on the volume pot the amp starts squeeling and sounds real fizzy. Obviously without the ground the volume doesn't work correctly. Leaving the ground off makes the amp sound better but still distorted and farty..

I know it has to be a ground issue that I don't see.
I have tried a seperate 1M pot, I soldered a ground strap to the 500k body and still the same.
I tried an isolated seperate input bypassing all resistors and going straight into V1 #2 no change.
2 ground lugs near input, v1 and pot...the board, pot, input Jack all ground on one bolt with 2 solder lugs.

Title: Re: Ugh.......been here a while but first post. Champ circuit.
Post by: Latole on June 14, 2021, 03:41:55 am

Show us a good pictures of the amp.

And schematic as built

Title: Re: Ugh.......been here a while but first post. Champ circuit.
Post by: Stuff4bikes on June 14, 2021, 12:58:24 pm

I got it! ...I am using salvaged parts from an auction and the output transformer primary wires are both black, so I reversed them and all is well.

Title: Re: Ugh.......been here a while but first post. Champ circuit.
Post by: Latole on June 14, 2021, 01:19:46 pm

Great !