There's some preposterous stuff on here -- first of all, the amp (Orchestra Reference) IS NOT autobias. And, autobias IS NOT a step up -- it sounds worse than fixed bias almost all of the time (because you are listening to an extra capacitor).
The easy way to bias these amps, if you can work with 550v without killing yourself (and if you cannot, do not) is to:
1. measure the output tube plate voltage to ground.
2. measure the output tube cathode voltage to ground (should be about zero).
3. look up the negative bias voltage for the output tubes you use, at the plate voltage measured, on the tube curves available at duncanamps.com or elsewhere.
4. find the grids of the output tubes and measure the voltage there.
5. adjust the bias pot that corresponds to the grid you are measuring, until you set the voltage you need as found in step 3.
6. Check twice.
7. Wait 30 minutes with the amp on, input shorted, output loaded with 8 ohms or speakers.
8. Check and adjust again. If there are any bias changes more than a volt, wait another 30 minutes and check again.
9. If after three such checks you are still getting voltage changes, you need different output tubes.
If any of this sounds strange and unfamiliar to you, STOP and find someone to whom this does not sound strange and unfamiliar, to do this work.
The easy way to bias these amps, if you can work with 550v without killing yourself (and if you cannot, do not) is to:
1. measure the output tube plate voltage to ground.
2. measure the output tube cathode voltage to ground (should be about zero).
3. look up the negative bias voltage for the output tubes you use, at the plate voltage measured, on the tube curves available at duncanamps.com or elsewhere.
4. find the grids of the output tubes and measure the voltage there.
5. adjust the bias pot that corresponds to the grid you are measuring, until you set the voltage you need as found in step 3.
6. Check twice.
7. Wait 30 minutes with the amp on, input shorted, output loaded with 8 ohms or speakers.
8. Check and adjust again. If there are any bias changes more than a volt, wait another 30 minutes and check again.
9. If after three such checks you are still getting voltage changes, you need different output tubes.
If any of this sounds strange and unfamiliar to you, STOP and find someone to whom this does not sound strange and unfamiliar, to do this work.