MGW wrote: Would putting two pairs of 1n4007 diodes instead of just the pair make a difference?
120Hz is a fundamental of the main frequency, adding another rectifier diode in series has no bearing. Now if it's truly 120Hz hum, you need to be looking post rectification and looking towards the B+ filtering and grounding scheme.
Honestly, it hard to tell what's going on from the pics. Can you make a block diagram of how the amp is grounded?
FYI, the proper way to ground a lug to a chassis is: pass screw from opposite side>chassis>ext tooth lock washer>lug>nut
MGW wrote:I built a JCM800ish head, basically and Egnater seminar head. And I can't get the hum out of it. Bruce has been kind enough to help me with a lot of stuff on the amp, but I have rewired the amp twice, rewired the heaters 3 times, swapped out the tubes more times than I can count.
Is it possible that the PT is introducing noise somewhere? Is it possible that I have a bad PT...if so, how do I tell?
Is there anyone in the Dallas/Fort Worth area with a scope that would be willing to help me track down the hum. I'll bring beer...or other beverage of your choosing
Are you grounding to the chassis? Try a correct grounding scheme.
Don't ground to the chassis except at 2 places one for audio and one for 3rd pin at least 2 inches away from each other. You can not control ground currents in a chassis.
John, if you don't count the bus wire on the pots where everything is grounded, I've only got the earth from the 120VAC (which is actually about 125 here in Fort Worth. And I have spoken to the delivery company about it. I am hitting about 505vdc at the first cap), and the ground for everything else it a couple of inches away. The cap for the preamp nodes is grounded on the bus wire.
Bruce sent me the schematics and I pretty much copied his layout from pics that I managed to get my hands on. Should I removed the buss from the back of the pots and suspend it on lug 3 of the pots? It's quite tolerable until I really crank it.
I'm gonna rework the topology of the preamp and add a 4th stage. Something close to a 3rd channel of a 3+.
