New KT150 tubes?

@Wolf .... of course not Wolf. Many reputable vendors match tubes. It just happens to be IME that ARC matched power tubes bias much easier in my amp. Btw, for the sake of clarity, I am referring to KT-120s.

As an fyi, my amp has a bias "set" tube and a "slave" companion for each pair of tubes, which are configured in push-pull topology. The way the tubes are biased is that I can adjust bias (65 mV)for the set tube, but not the slave.

If the tubes are well matched, the slave will show a bias voltage ranging between 57 mV and 73 mV. If the slave tube bias is out that range, the amp will not operate within spec.

As I said, even though I have bought "matched" tubes from private venders, sometimes the slave doesn't fall within the spec range. IME, this hasn't occurred with ARC spec'd tubes.

Now, as to the KT-150s, that's right, ARC has not blessed using that tube ... yet. Will it work?? Dunno. Some have tried it in their ARC amps and report great results. Will it hurt the amp? Dunno. Will just have to wait for ARC to approve the tube.

Wolf ... like most A'goners, my gear represents a significant monetary investment. In particular, my amp is a pricey piece of kit. Maybe I'm just being over-cautious, ... but until ARC says the KT-120 will not damage my amp, I'm not experimenting. I will defer gratification.

Cheers.

I purchased a quad of kt150s from uncle kev at upscale.

I've had them in my primaluna prologue premium integrated for about three weeks now, replacing the stock el-34s. Wow! what an upgrade. Finally giving me that deep bass punch; it struck me like I bought a new amp when i dropped the needle on Talking Heads Stop Making Sense. At the same time all the sweet midrange is still there.

Absolutely no issues. The tube cage does need to be removed

There seems to be some confusion regarding 120s or 150s, and I like it.

Can I ask a stupid question, plainly, 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?

I agree with Bifwynne, I am not going to put KT150's in my ARC ref 75, until ARC says it is ok. It is the most expensive bit of kit I have ever bought and I can't afford for it to go up in smoke, or to void my warranty, by making the change.

In fact I have just bought a really nice 2nd hand Skoda car with low mileage. With a trade in, it cost about the same as the ARC. It makes you think how your sense of what is good value, can get a bit warped, in this hobby. Not that I am complaining about the ARC, it is a wonderful amp, I hope to be still using in 15 years. I suppose it's a question of which one of us blows a capacitor first, sobering thought

@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