Stereomour bias instructions

[dpwoos]

We are seeking the procedure for biasing our Stereomour amp. The cd that came with the kit has gone missing, and the manual doesn't seem to be available on the web? Thanks.

 

[Paul Birkeland]

There are no biasing steps, the amp is self biasing.

 

[dpwoos]

Thanks for pointing this out. In fact, my son built this amp and so my understanding is limited. Is there a procedure for setting these hum pots (that I incorrectly assumed were for bias)? I am also looking for a manual.

 

[Mike B]

1)  Disconnect speakers and sources
2)  Turn on amp and let it warm up
3)  Short out the input to one channel
4)  Put AC voltmeter on that channel outputs
5)  Adjust humpot for lowest reading on voltmeter
6)  Repeat 3-5 for other channel.

 

[dpwoos]

I am surprised that it is OK to run without speakers, as I thought that doing so was not good for the output transformer? Thanks.

 

[Paul Joppa]

It gets posted fairly often, but not everyone sees every post!

Most tube amps are pentodes in push-pull Class AB or B and with substantial global feedback. The feedback carries the risk of instability and destructive oscillations if they are not properly loaded. Pentodes have a high output impedance which allows them, in conjunction with the transformer's inductance, to generate very high voltage spikes if they are not properly loaded; operation outside Class A makes this potentially worse. (This last is similar to how the spark coil works in a car, generating 15,000 volts from a 12-volt battery...)

Our amps are triode amps in Class A with zero feedback. Such amps are essentially immune from the instability and uncontrolled voltage spikes described above.

 

[dpwoos]

Great info - thanks! I did the adjustments as described above.