Biasing VH4: procedure with bias adapter?

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jswevers

jswevers

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Biasing VH4 power tubes: is this the right procedure (I could not find the procedure anyware)?
- remove chassis from housing
- replace existing tubes with a matched quad (eg JJ KT77)
- Place a bias adapter (the one from Tube Town) in between amp socket and one of the tubes and connect a DMM, put it on the 200mV range
- connect cab as usual
- switch on the power of the amp, a bit later the stand-by ON, master on ZERO
- read out the DMM and turn the bias pot until the reading is about 35mV (corresponds to 35 mA)
- I assume that that is all since there is only one biad pot and all tubes are matched ... or is there more than that?

Correct or not?

Thanks

Jan
 
i think there is just one.

i would first turn down the bias pot a little before switching the amp on since you don't know if the new tubes are the same as the old.

i also marked the bias position while using the old tubes, because i carry them with me as spares... i can now put them in and use the old bias position if i have to change tubes quickly during a concert ('s break).

while biasing the new ones i also turned up the bias pot until 30mA on the first tube and placed the bias adapter under every tube (with the amp switched off while changing of course) to find out which tube draws the most. but i just did that out of curiosity.
 
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