Newbie Biasing ARC Amplifier Queries

[artoly]

I’ve owned my first valve amps for a little over a year, being an ARC Ref110 power amp and Ref3 preamp, so need to lean to bias them. I would appreciate some absolute beginner info. Apologies in advance for the simplicity of the questions to everyone here who has done it 100's of times.

1/ My understanding is that only the power amp output tubes need any attention. This understanding is due to the lack of any instructions in the manuals for the other tubes. (Meaning no biasing or maintenance required for the preamp tubes at all and none for the 4 input tubes). If I have this wrong, I would be grateful for a correction.

2/ The Ref110 manual is for ‘a nominal 65mA per 6550 tube’. Does the 65mA also apply to the installed KT120 tubes?

3/ It also states to ‘adjust the Reference110 at 120VAC’. Does a different country voltage affect the 65mA setting? I run mine at 230V.

Post edited as was too long.

4/ Any other tips for a newbie? (apart from not touching anything else and zapping myself, which goes without saying :-0 )

 

[artoly]

My post was too verbose, so edited to be a bit more to-the-point.

 

[tuber]

65 mA is also correct for KT120s. Bias at your normal line voltage.

 

[Pacha]

In a similar situation, ARC Ref 150 amp that came with KT120 tubes, when I chose to upgrade to KT150 tubes, I contacted ARC and they told me to keep the bias at .65 ma that the KT120s were at for the KT150s.

 

[artoly]

That's interesting @Pacha . It keeps it easy anyway. Their is a reviewer who also had KT150's in a Ref110, but I don’t believe it is recommended. The Ref150 would be a better match for my speakers. One day perhaps.

 

[microstrip]

Remember that the ARC REF150 needs plate current matched pairs of power tubes. You bias one tube of the pair and the other tube uses the same grid bias. The bias of the slave tube should also be checked to be sure it is inside the tolerance interval.

 

[artoly]

It's amazing how much we can learn from online video these days. How to bias is sorted, but I did need a better expert to help fix a pot that wasn't dialing it down correctly.