Ceriatone Expression bias question

[Riley]

Forgive my lack of knowledge but here’s my question:

I have a used Expression I bought a while back, I got bored one day so I pulled the chassis to change the power tubes and check my bias. I use a Weber Bias Rite unit.

I check the bias voltage on the KT77's that were in it and they seemed way off and very low, like 29 mV. So I put a new set of Mullard reissue El34's in it. When I use my Bias Rite from Ted Weber the plate voltage was reading 191 per EL34 tube, so that's 382 volts total correct? Which is what I use to determine where my mV readings should be per tube at 70% dissipation right? If that's right...... from my calculator I needed around 45 mV per tube. I got one at 45.5 and the other at 43.5 so that's not bad. Seems to sound ok I think, maybe better than it was. KT77's are basically EL34's so I dunno why the guy I bought it from had his mV bias so low.

Thanks.

[leaveitalone84]

Maybe he thought it sounded better.

I set my bias by meter for 70% then adjust by ear.

[Bob-I]

In Ken Fisher's "Train Wreck Pages" in Gerald Weber's book, Ken states that bias can be 10-50ma. He believes that you can get a more consistant sound by setting the bias voltage, C-, rather than the bias current. I don't know that I completley agree, but who can argue with Ken

Basically 29ma is fine, so is 45ma. Adjust to your ear.

[Riley]

In Ken Fisher's "Train Wreck Pages" in Gerald Weber's book, Ken states that bias can be 10-50ma. He believes that you can get a more consistant sound by setting the bias voltage, C-, rather than the bias current. I don't know that I completley agree, but who can argue with Ken

Basically 29ma is fine, so is 45ma. Adjust to your ear.

Thanks Bob. Good info to know.