Biasing Uber Ultra

leib10

leib10

Well-known member
Quick question for Uber Ultra owners out there. I had a Twin Jet previously, but the external bias points are different on that amp. Using a multimeter, do I put the negative (black) lead in the point labeled Ground and the positive (red) lead in the points labeled V7, V8, etc.?

Also, are the matched pairs V7 and V10, and then V8 and V9? Thank you!
 
leib10 said:
Quick question for Uber Ultra owners out there. I had a Twin Jet previously, but the external bias points are different on that amp. Using a multimeter, do I put the negative (black) lead in the point labeled Ground and the positive (red) lead in the points labeled V7, V8, etc.?

Also, are the matched pairs V7 and V10, and then V8 and V9? Thank you!
Click to expand...



I have a UU as well. Thats is correct.
 
Since we are in the subject, do you have a reference on how to actually adjust the bias?

I don’t have experience with electrical circuits, but my understanding is this is one of those things you can learn to do without 10,000 hours of engineering experience.

Expecting to take delivery of my UU in about a month, and I’ve heard that they sometimes show up biased a little off.
 
There are two pots on the exterior of the chassis, one that controls the bias for V7 and V10, and the other for V8 and V9. I think Bogner biases their EL34 Uberschalls at 25 mA, which is fairly cold. I usually biased my earlier Uberschalls at like 30-32 mA (about 60% dissipation).
 
leib10 said:
There are two pots on the exterior of the chassis, one that controls the bias for V7 and V10, and the other for V8 and V9. I think Bogner biases their EL34 Uberschalls at 25 mA, which is fairly cold. I usually biased my earlier Uberschalls at like 30-32 mA (about 60% dissipation).
Click to expand...


50% is not too bad and is typical what amp companies set the bias at. For a higher gain amp, you don't want the power tubes to be too soft sounding with a hot bias. 50% is kind of a middle of the road bias setting. The bias points on the Bogner's are using a 1 ohm cathode resistor, so you're measuring both screen and plate current.
 
leib10 said:
There are two pots on the exterior of the chassis, one that controls the bias for V7 and V10, and the other for V8 and V9. I think Bogner biases their EL34 Uberschalls at 25 mA, which is fairly cold. I usually biased my earlier Uberschalls at like 30-32 mA (about 60% dissipation).
Click to expand...
@leib10 ... dont forget to measure ya voltage at pin 3.... the plate voltage also plays a factor ... P= VI
 
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