bias experiment?

jemke · #1 03-13-2005, 09:44 AM

Does anybody has experience with changing the bias of your tubes and the effect on the tone? I have a marshall JCM 800, it has just one pot to change the bias voltage and is set up in the middle between high and low bias voltage. Is it safe to turn it up or down and what are the advantages and disadvantages in tone and tube life?

Rotti · #2 03-13-2005, 11:46 AM

I don't think you should adjust it. There is a range in which it's safe to adjust but if you run it too hot you risk damaging your tubes and amp. You really need someone with the knowledge and the equipment to make the adjustment.

yannvii · #3 03-13-2005, 10:56 PM

Do the guys at the guitars shop can do this?
Or I need to ask a technician?

RSVampire · #4 03-14-2005, 05:58 AM

Quote:

Originally Posted by yannvii

Do the guys at the guitars shop can do this?
Or I need to ask a technician?

definetly want a tech, most guitar shops send them out to tech's anyways.

jemke · #5 03-14-2005, 03:21 PM

OK. So it is not safe to assume that the pot to change the bias was dimensioned in a way it can not harm the tubes...stupid amp designers.
Does it can only harm your tubes or also sometning else like resistors and capacitors? If its only the tubes...wtf, they're already old.

Rotti · #6 03-14-2005, 04:09 PM

I'm no expert but I was told recently when I had my bias adjusted that it can damage the tubes AND the amp. You can damage your power transformer, and maybe some other stuff. I'm not 110% positive about this but it's not worth finding out. The bias is adjustable to compensate for different types of tubes, and even different tubes of the same type can differ quite a bit in adjustment. Leave it to the pros.