Any knowledge would be appreciated.
I don't know how long it has been going on, the left side of my VHT2150 (2 independent 100watts power amps) power amp works well and sounds good, but there is a noticeable low hum coming from the speaker on the left side only. When I tap the front panel which is made of metal, I can hear the metal clanking as if something was picking up the sound of the knock from the inside, so I'm guessing either one of the Power Amp tubes OR the Pre Amp tubes (there is one 12AU7 and one 12AX7 on each channel).
Now, if I understand correctly, I should open it and start knocking gently on each tube with a pencil while the amp is on right? If it's a preamp tube I can just swap it myself and it's done. But if it's a Power tube, ugh I'll have to carry that brick to the tech and wait a week and a half for a retubing-rebiasing, hell.
Also, can playing on it damage the amp circuit?
Apart from hearing that low hum it doesn't affect the tone at all so I might tough it out, I'm hoping it's not the Power Tubes cause those KT88 are expensive and taking it to a tach for re-biasing is a pain in the ass.
Tapping on the tubes will sometimes find the bad one, but not always.