Blowing fuse and hum from an effect loop

[martin manning]

With V2 removed, what AC voltage do you see on socket pins 1 and 6? Should be ~0 VAC.

[bluescaster]

0 VAC

[martin manning]

So adding V2 brings on the hum, and the supply voltage at that point is clean (no AC). I'm still wondering about the heater cathode insulation. Are you sure that the tubes you have tried in that socket are good?

To see if the hum is coming from V2b, you can try taking it out of the audio path. Disconnect it's anode and cathode leads at the socket and connect the tone stack input to the anode of V1a. It would be best to use a cap to block DC from the V2b Rk.

[bluescaster]

If i put one of the red arrow to ground, hum disappear. No effect when i do the same on blue arrows, even if i put the 3 arrows in the same time to ground.

[IMG:200:162]http://www.image-share.com/upload/2962/137m.jpg[/img]

[martin manning]

If i put one of the red arrow to ground, hum disappear.

This means the hum enters before V2, since grounding V2a's grid kills it.

No effect when i do the same on blue arrows, even if i put the 3 arrows in the same time to ground.

Do the volume pots affect the hum at all? If you ground either or both of the volume pot wipers is the hum affected?

In your photo the heater wires going to both V1 and V2 are not very tightly twisted, and pretty close to the grid wires. Maybe cleaning that up will help.

[bluescaster]

I'm gonna to remake heater wiring. Something i don't like to do

[bluescaster]

Hi,

Heater wiring it's ok now. Less hum.

I plugged amp in an other outlet and then, no hum !!! I don't understand how it's possible ?

Thank you for the help.

[martin manning]

An open chassis can easily pick up stray EMF. Fluorescent lights or dimmers nearby? Did you move to another room?

[bluescaster]

No, just another power outlet on the wall. My Tweed Deluxe that is very silent, buzz too on this outlet.