2. amps-preamps
  3. 1145456950

Biasing amplifiers

Hi, I am new to biasing amps. Just trying to understand how accurate one needs to be in matching the bias.

At present i am using 300B monoblocks & have WE300B tubes in them, bias set to 65mA. Now I have noticed that this varies somewhat between say 64.5mA to 65.1mA however i try to set this at the exact 65mA mark. This is on one amp & the other varies on it's own near +/- 65mA. So if you look as a whole BETWEEN the amps you may even end up with more than 1mA diff.

What is an expectable varience range one can expect when biasing an amp? If the diffrence between amps vary more that 1mA, for example, what neagtive effects can it have on the sound?

Thanks.
dilly

Showing 1 response by newbee

newbee
4,751 posts
 
Bias drift occurs for many reasons, the tubes themselves can cause drift, the condition of the amp, and even its design can cause drift, and the time in use can cause drift.

It also depends when you measure - many amps will have bias drift during warm up continuing on 'til everything is warm and stabilized. Some amps will drift downward with excessive continuous use.

1ma is not(!)a big drift unless you are extremely anal. :-)
More to discover