Biasing EL34 Amp ?

CA$H FLOW

Member
Messages
947
My Traynor YCV50 has a bad power tube, already figured that one out. I have a matched quad of KT77 tubes, a Garbner Bender multimeter and a eurotubes bias probe.
Considering that my tubes are all matched I should only have to use the bias probe on one of the tubes while adjusting the trim pot correct ?
The manufacturer suggests setting the zero signal bias to +75mV, now is that number divided by the number of power tubes ?
What setting do I need to set my multimeter on ?
Do I need an insulated screw driver in order to adjust the trim pot on this amp?
Do I adjust the bias in standby mode? Or On ?

If you can please answer all the questions as I do not want to harm myself. Thanks!
 

Blue Strat

Member
Messages
30,066
My Traynor YCV50 has a bad power tube, already figured that one out. I have a matched quad of KT77 tubes, a Garbner Bender multimeter and a eurotubes bias probe.
Considering that my tubes are all matched I should only have to use the bias probe on one of the tubes while adjusting the trim pot correct ?
Yes, but rather than assume anything and possibly be wrong, check them all since it takes an additional minute.

The manufacturer suggests setting the zero signal bias to +75mV, now is that number divided by the number of power tubes ?
Hopefully, because that would be way high for one power tube, about right for 2 tubes combined.

What setting do I need to set my multimeter on ?
Whichever one is over 75mV by the least amount. Standard settings might be 200mA or so.

Do I need an insulated screw driver in order to adjust the trim pot on this amp?
I can't speak for that particular amp, but generally you don't. But it definitely couldn't hurt because if your hand slips, in any amp, a non insulated screw driver might short something out.

Do I adjust the bias in standby mode? Or On ?
Definitely on. You won't get any reading at all in standby because the tubes won't be conducting.

If you can please answer all the questions as I do not want to harm myself. Thanks!
Good call on your part to ask questions first.

Before you do anything with the NEW tubes, try adjusting the bias on the old tubes until you feel comfortable.
 

flcmcya

Silver Supporting Member
Messages
3,423
Thanks for asking questions....Blue Strat's right on.

First off Bob (Eurotubes) has some decent biasing Vids on his website....

Second ...Posts like this work better in the amp tech section......

Third...... I highly recommend you get someone to help you do this the first time...as you know there are dangerous voltages inside of an amplifier :omg and more to it than just plugging in and dialing up a number.

Try some light reading over at the Amp Garage site ....a lot of good resources and information. :beer
 




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