Blown screen resistors and more

[drew]

You can run the artificial center tap resistors from the indicator lamp terminals to a solder lug under the closest PT bolt. Example: http://el34world.com/Hoffman/Princeton_ ... _Build.htm
(This is assuming your amp is still using a standard Fender lamp.)

[titser_marco]

You can run the artificial center tap resistors from the indicator lamp terminals to a solder lug under the closest PT bolt. Example: http://el34world.com/Hoffman/Princeton_ ... _Build.htm
(This is assuming your amp is still using a standard Fender lamp.)

Ah, that's the thing. It's currently using a 220v pilot lamp.

[Phil_S]

3) My heater taps do not have a center tap, so my tech advised me to ground one of the heater taps. Currently, it's grounded to the chassis. Should I use the 2x100ohm grounding resistors on heater taps, and then ground it to where the PT ground is attached?

This should not share the audio circuit ground. The ground point can be at any convenient spot on the chassis.

[titser_marco]

So I put in the heater tap resistors (150ohm, 100ohms was out of stock) and the hum was minimized.

Now I noticed that the NFB resistor was disconnected so I resoldered that. Lo and behold the hum was GREATLY minimized. Now, the amp only has that his at max preamp and master volume and a very low level 60hz hum at zero preamp volume but max master volume. So I guess my question is: is it possible to have a 100w guitar amp with no NFB to function without hum?

Another thing: I'm finding it strange that the 60hz hum is loudest when the preamp volume pot is at the middle. Could this be a pot issue rather than a grounding issue?



Thanks!