New KT150 tubes?

@David12, you asked "if you are using an auto bias amp, you need a matched pair or quad of tubes. If you are using an amp, like the ARC power amps, where you have to set the bias yourself, does it matter if they are matched or not?"

Yes, ... I think it does matter for the reason I explained above. In both the ARC Ref 75 and Ref 150, each tube pair has a "set" tube and a "slave" tube. As you know, only one tube, the "set" tube takes the bias adjustment. The "slave" tube bias has to read between 58 mV and 73 mV in order to be in spec. So matching is important.

In addition, and this comment (or better, "guess") is best expanded on by techs like Gary (Hifigeek1). Gary is an authorized ARC service tech. That is there may be other electrical parameters that should be matched, like power output. Obviously, if that is a key spec, I intuit that in a push-pull configuration, if tube output power doesn't match within spec, the waveform could be distorted. I'll stop there because I am now way north of my pay-grade.

Bruce

Traded some e mails with Kal at ARC. He reported that ARC is still doing life testing on the KT-150. Kal declined to provide any further information or advice. That's all there is to report.

Wait...it's been another 2 days of waiting for Kal's testing results...I can't handle the suspense...I'm in audio LIMBO...

Ok. I have similar concern.
Have an aplifier designed to work with 6550/KT88 family of tubes.
Now I have KT120 installed - ok by manufacturer.

I was considering using KT150 im my amplifier, but manufacturer adviced not to do so. The point is not that both KT120 and KT150 have almost the same current draw. The point is different characteristics (curves) in KT150.
When used in amplifier with plate voltage lets say - 485 V and fixed bias point using KT150 will lead to use the tube in non optimal characteristic point (not the most linear part of characteristic). This is at least explanation I got from amplifier manufacturer.

Using KT150 in their optimum requires output transformer to be specially wound for them as well as setting proper working plate voltages.

Milimetr ... that's a great explanation. I'm sure the factors you describe are (or were) also under consideration by ARC.

Quite honestly, I'm not sure what "life testing" entails. Perhaps it involves running the tube in actual operation in the amp to check if it has a deleterious effect on other components. It might involve long term subjective sonic testing. Not really sure.

That's why although I am personally interested in following the outcome of ARC's testing process, I'm not so curious to plop those tubes into my ARC until ARC gives the green light.