VVR Hum

[MarshallPlexi]

Guys this is my VVR supply and I'm still getting a lot of 120Hz hum out of it at all volume levels. I can get less hum by adding more filtering (100uF+) after the fuse but 60uF is as far as I can go with a tube rectifier. Anything I'm missing here?

[MarshallPlexi]

Figured it out. The VVR needs more filtering before the input of it so as a test I hooked up a 47uF cap out of the tube rectifier and ran that through a choke and then into the VVR. Dead quiet. The DC resistance of the choke was 350R so I lost a lot of voltage but that gave me the idea to try a resistor instead of the choke. You know the old Trainwreck Express trick of using a 1k resistor instead of a choke thing?

Well I wired up a 500R wirewound pot and adjusted the value until the hum just stopped. The value was 150R. So doing the math to find out how big of a resistor to put in there to make sure that the B+ fuse (.5A) dies first in a dead short situation, I found that the 150R resistor at .5A would dissipate 35W of power so I installed a 150R/50W resistor that I had lying around and it's all good now.

I did lose 30V of DC out of the tube rectifier but that's fine. I wanted to lower it a little.

I'd like to thank me and all my hard work for helping me figure this out.

[ampgeek]

Well done mate!

Nothing like that feeling of accomplishment you get when you ferret out the solution to a problem on you own.

Cheers,
Dave O.