ARC Reference 150 Tube Biasing Issue

Scott, I doubt you will damage the amp. But it may be making some distortion because the one tube pair is a little out of spec.

Here's another idea ... focus again on the other 3 tube pairs. With the set tubes biased to 65 mV, is there any slave that is between 57mV and 60 mV? If so, switch the 78 mV slave with the other low mV bias slave. Check bias again. Incidentally, spec is between 57mV and 73 mV.

And btw, you should always let the amp sit for at least 5+ minutes between turn-off and turn-on. You could damage the amp if you don't wait a little. The power supply caps need to discharge a bit.

Another thought if the idea above is a non-starter is consider buying just one matched pair set from Kevin Deal at Upscale. IME, Kevin does not match as closely as ARC, but he's also half the price. He may get you closer than where you are now.

Please let me know how you make out.

Bifwynne, thanks. I will try the procedure you suggest on Saturday.

Scott, just a thought for the next time. I am not an electronics tech, but many members happen to be. Perhaps one of them will jump in.

It is my understanding that ARC, and perhaps many other manufacturers, recommend using matched tube pairs for their amps. And this is where the experts can chime in ... matching entails more than just buying tubes which happen to bias closely. There are other electrical attributes that are taken into consideration when matching tubes, for example, transconductance, G2, resistance, microphony, and so forth.

I really do hope one of our other experts will jump in now. So my point is that if my thoughts, as expressed in the preceding paragraph are accurate, that should encourage you to buy power tubes from reputable sources, such as ARC, or Upscale Audio, and the many other fine tube vendors out there.

Btw, surf through the Upscale web site. Uncle Kevin talks about his tube testing and matching procedures.

Cheers,

BIF

Does anyone buy RAM tubes anymore?