Amp bias ?

[hamerican gigolo]

I have a Princeton Reverb clone. It is fixed bias with an adjustable pot. It reads 410 volts across

the plates. My tech used a Weber Bias Rite & set it for 70% idle plate dissapation. It read 20.4

mils on the meter. My ? is,does that sound right? A couple of friends of mine who are blues players

said they could be adjusted a little hotter. Any help or opinions at all would be greatly appreicated.

P.S. I forgot to add that these are Tung-Sol reissue 6v6 power tubes bought new.

[edgar_allan_poe]

Go here...

http://www.webervst.com/tubes1/calcbias.htm

This is what I use to get a *basic* starting point.

20.4 sounds right to me, but turn it up a little hotter and see how it sounds. Remember that you sacrifice tube life if you do that though.

[zenmindbeginner]

I don't know if your Princeton clone is wired like the Blackface Princetons, but the Princetons use the bias to get the vibrato sound. If your vibrato is thick and rich, then you have the bias set right. If the vibrato is thin and anemic, then you have the bias set too high. A high bias will constrict the tone, lowering it to the proper level should "open it up" a bit.

At least this is what my tech told me when he set my Dad's 1966 Princeton's bias a few months ago (I got his amp serviced for his birthday.) The bias was set a little hot and the amp sounded sort of compressed as a result... the vibrato sounded compressed too.

But when he set the bias lower, the amp sounded absolutely AMAZING and the vibrato pulsed and breathed like a DREAM.

Watch the vibrato pots since they are in the bias path. If they are scratchy, they can seriously wear out the power tubes.