Problems with Herbert microphonic

[Timonac]

Hi there,
i got an Herbert for a few weeks now, and played it the first time in a band practise....sound is great, but it is increadible microphonic. my bandcollegue got a vh4 and it is not microphonic at all. i checked out differnt guitars...no difference. still microphonic.
wht is the problem here ?

 

[White_Van]

Tubes. Check your preamp and your poweramp tubes. Not really sure which, wait for the mastermind himself to chime in, he'll set it straight.

 

[Lexicon Devil]

The first two tubes( V1 &V2) in the signal path from your guitar are usually the culprits, as all the tube that come after them amplify the signal from them. Out of those two tubes, V1 is usually the culprit.

A surer way to confirm this though, would be to remove the amp chassis from the head sleeve and place it on a flat surface like a table or a desk which is isolated from the speaker cabinet. Hook the cabinet up to the amp and turn the amp on. Find a chopstick or wooden ruler and LIGHTLY tap the preamp tubes. You should hear a plinking sound on the bad tube, though this may be evident on all of the tubes in this amp, as the 12ax7's are PCB mounted, which means that the vibration will carry to all the tubes. The tube with the loudest *plink* would most likely be the culprit. --If it starts to squeal, you'll know even further that you've found your problem.

You may be able to move the bad tube further down the signal chain, and closer to the PI tube and solve the problem. If not, buy another tube. --If it's V1, you'll want to make sure that the tube you buy is selected and tested for low noise which will add a few dollars extra to the cost of the tube.