Biasing for new tube

Thanks for all of the help; my first attempt at checking bias and re-setting bias were successful -- and no injuries were sustained!

Mmaudio - As I understand it, any current/signal/input at the terminals may alter the readings. Some folks recommend simply turning the volume all the way down on the preamp, or shutting it off. I've was taught that the safest way was to simply remove the connection altogether.

Jax2,

Forgive me, but as a newbie at tube biasing myself, why do you recommend removing the interconnects before biasing?

mmaudio

I always turn down the bias on the old tubes before I put in the new tubes.Your old tubes do get tired and need more of a push ,so when you put in your new ones they shouldn't need as high a bias....This works for me...

Yes you should certainly re-bias installing a brand new tube in your tetrode amplifier. Your amp does have a bias setting for each tube. You may want to turn down the bias setting on the new tube before turning it on just to be on the safe side, though it is not very likely doing otherwise will do any harm (in case you already have). The bias setting for the tube that arc'd is not likely going to be the same as that of the new one, and it is better to start lower and go up rather than put undue stress on the tube (in the case that it was set much higher than the new one requires). As I recall, VTL amps bias rather high, and put more stress on tubes than other amps so it would also be worth biasing the remaining five tubes. Keep the speaker connection, but pull the interconnects from your preamp out before biasing. ALWAYS keep the speakers connected if the amps are on. Allow all tubes to warm up sufficiently before biasing any of them. 3 minutes or so ought to do it. Bias the new tube, as Newbee said, according to VTL specs to match the others in the set.

Check the bias on the new tube after a few hundred hours of play time as well as it may vary slightly as it breaks in. I used to check my tubes about once a month when I had manually biased amlifiers, and a bit more frequently when tubes were new. This worked for my Quicksilver amps that required biasing, as well as the Mesa Baron I had. Some amps are less stable than others and may require more frequent attention. Check with VTL for their recommendations, and see what your own experience tells you. Keep a few spare fuses on hand for those pesky arc'ing tubes as well.

Marco

Don't know about VTL but most tube amps provide for individual biasing of tubes and you should set the bias for the new tube at the same setting as the other tubes in the set.