5F6A Noise problem

[philster]

Have videoed the amp making the noise - hope this sounds familiar to someone? A friend suggested I remove the grid wire from V2 to see if it had an effect - it didn't, the noise still appeared. He suggested I probe with a cap to ground at the cathode and plate to see if it helped - again, it didn't.
Any thoughts?
Cheers
Phil

https://www.youtube.com/watch?v=0-vrmZR ... AVcwJ7LaxA

[philster]

I reflowed all the solder joints on the board and also went through the sockets - instant I turned the amp on there was the noise

So - I am totally at my wits end. I have replaced most of the components except for the trannies or choke. The noise stops if I pull V2 or the PI tubes - has no-one ever had an amp with a similar issue? I really need help here Amp Garage!
Cheers
Phil

[Reeltarded]

Sounds like a gravel truck!

Hold on. Everyone starts getting off work soon! heh

[Stevem]

I took a listen and it sounds like a tube socket arcing or a bad plate load resistor, or a very leaky coupling cap.

Starting with V1A and going down stream ( V1B, V2A and such) unsolder the and lift each plate load resistor at its power supply end until you kill the noise and pin down where the issue lies!

[philster]

I've replaced the plate resistors already - that's the 100k on pins 1+6, yes?

[philster]

Steve - when I lift the plate resistor on V2 the noise stops. Still there with V1A and V1B.
I've replaced the tube socket and the plate resistor with new. When I tap the caps and resistors upstream I get no noises - is it worth replacing the caps in the tone circuit?
Cheers
Phil

[Reeltarded]

Turn out the lights and watch for flashing or slight dimming of a tube when the noise happens..

Hmmm

[martin manning]

when I lift the plate resistor on V2 the noise stops. Still there with V1A and V1B.
I've replaced the tube socket and the plate resistor with new. When I tap the caps and resistors upstream I get no noises - is it worth replacing the caps in the tone circuit?
Cheers
Phil

So you know that V2a or V2b or something downstream is causing the noise. See if you can kill it by grounding the wiper (center lug) of the treble pot. If so then you've determined that the problem is in the tone stack. If that is the case, I would first try replacing the 250pF treble cap.

[philster]

Reel - just the power tubes flash in the dark.

Martin - many thanks, just grounded the wiper of the treble pot and the noise stops (in fact all sound stops!) When I pull the clip the sound returns. Will swap out the cap right now

[Reeltarded]

In rides the cavalry.

[philster]

I'll say!!!!! Have swapped the mica cap out for another and so far so good. Will give her an hour sitting there quietly - if no more noise then we have a winner!

[Reeltarded]

You had already asked the right question.

Martin rocks it most every time.

[philster]

Well see's been quiet since I swapped the mica so I guess that was it. Many, many thanks to all for the help, especially Martin - I was genuinely at the end of my tether this morning over the amp and now she is back. Thank you!
I guess the good news is the amp won't need new caps for quite some time
Thanks
Phil

[martin manning]

Cheers, Phil! You were most of the way there with the suggestions from others. Troubleshooting is art, science, and educated guessing. In this case there was a little "dielectric profiling" too ;^)

[philster]

Ha! Yes, reading back through I had all the answers. It's rather easier in "hindsight mode"....
So pleased she's back though - I've borrowed a solid state Fender combo to get through the last bunch of gigs and oh my, it's fine for clean but overdrive is a different matter. When you put pedals in front of the Bassman it's like they are part of the preamp, if that makes sense?
Right - stress fading away, smile on face. Thanks again Guys!
Phil