Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bruno on February 28, 2012, 06:42:33 am

Title: 1965 Vox ac30 hum...
Post by: bruno on February 28, 2012, 06:42:33 am

My vox ac30 still has some hum, while playing I doesn't really bother me too much, recording however is a problem.

I've changed the original filter caps, for new ones, but kept the same low values, as I feel that is part of how the amp feels and responds. I've also cut the heaters ground wiring which was done directly to the chassis, and used two 470ohms resistors to create a virtual center tap (might change to two 100ohms, but I didn't have them at hand).

the amp still has a reasonable amount of hum which obviously increase as volume does. I haven't started to change the power supply resistors (which probably have drifter somewhat in value), would that help?

Any other sugestions?

thanks

Title: Re: 1965 Vox ac30 hum...
Post by: rzenc on February 28, 2012, 07:55:08 am

Divide and conquer bro!

Take the P.I. tube out and check if it still hums...if so.. hum source might be after P.I.

P.S.: Check ALL ground tie points...had some hum issues going on due to inconsistent ground