Tube bias question.

madmax

So on my amp I set the bias to 40mV which means the high voltage is set to 400 Volts.

What would I be doing to the tube/volume/sound quality/whatever if I set the bias to maybe 30mV or 60mV?

madmax

PolknPepsi

Good question....

I would like to know too.

RuSsMaN

Over biasing, you will put stress on the tubes and circuit, and risk damage to the tubes and amp. Slightly under biasing will result in decreased performance (output). Grossly under biasing, and the amp may not function at all, with the circuit not seeing the voltage it is designed for.

Your Jolida should be able to take KT88's, which can be biased higher, for greater performance (output) - the design of the circuit and its components will determine by how much.

Cheers,
Russ

Early B.

Max -- just curious -- why do you set your bias at 40mV when the manual for the 502 suggests that it be set at 50mV? The reason I'm asking is because I've read on audioasylum that a few Jolida owners set their bias a little lower than recommended. Haven't tried that one yet. Just wondering what your results have been. Thanks.

madmax

Early B. wrote:

why do you set your bias at 40mV when the manual for the 502 suggests that it be set at 50mV?

Sorry, this was for the 302. Just playing with it last night. I think people set it just a little under what is called for to save tube life. Sure, if I had mullards or when I had the Blue Tubes in there I would obviously be concerned with tube life but with standard new issue stuff if I could get a little better performance I would go with 1/2 the tube life. I just don't want to mess up a transformer or whatever. I set it at 60ma and quickly played a short part of a song. It seemed more powerful.
madmax

Early B.

OK, thanks.

BTW -- can you send me your 302? I'd like to do a side-by-side comparison with my 502. Don't worry -- I'll send it back to you. You can trust me...