liverpool is whistlin

[aaronz28]

i've been playing my liverpool, and just came across a tube whistle... when I have the treble up or the bright switch engaged...

anyway I can verify which tube is the problem?

tapping on the all create about the same amount of microphonic noise, and I don't want to replace all the tubes... as it is vintage glass.

any help would be greatly appreciated
thanks


Aaron

[M Fowler]

I had a 12AU7 do that last night when I was testing tubes to keep or toss.

[funkmeblue]

do you have a known good 12ax7? If so try replacing each tube individually until the problem goes away. Or you could just try switching positions to see if the whistle moves or changes. It's more than likely v-1 as this is the most sensitive spot and what ever that tube makes will be amplified 100's of times over.

[UR12]

The PI (V3) is the least sensitive. Try swapping V1 with V3 and see if it goes away. If it does it was the V1 tube. If not then try swapping V2 with V3

[dartanion]

It could also be high frequency oscillation as you describe with bright switch on or treble turned up. Do you see the same thing when you crank the volume up, but more a squeal?

It's more than likely a microphonic tube though.

[tubedogsmith]

It's more than likely the tube but you want to have your bright switch wired with the middle switch wire connected to the pot wiper and the cap connected to the bottom lug on the switch and the input lug on the pot.