Audio Research Classic 150

im currently using a cl 150 and im quite happy w/ the performance of this amps driving my snell type A2 speakers. i find them more tube sounding than both my D79B one w/ 6550a output tube the other w/ kt88s, and also in comparison to my D250 mk2 servo.they sound musical w/ incredible imaging.the only problem is it goes to some sort of auto shut down ( i think its related to the tube saver circuit but im not sure about this) when the amp clips or when there is a sudden surge or spike in the power line.i use to bash the classic series amps when they 1st came out during the early 90s specially when they were using chinese 6550s. but when russian 6550s were use they sounded very good and i swallowed my pride and bought this flagship.currently using an arc sp10 mk2 to drive my amps.
theyre reliable and dont have regrets.

Sorry to revive an old thread... but I have to go out on a limb, as I own a pair, and to be honest, I'm in love. I have them on a Magnepan 20.1 system and they are fun to listen to. I think they do a fairly credible job of driving the 20.1 (i sold my 3.6 Magnepans before these arrived). They're sweet and very musically satisfying. Bear in mind that my room is small, but _in my room_, they sound terrific. There's something about Triode (or pseudo-triode, if you must) that is kind of awesome. (I have VTL MB-450 and MB-300s and love them).

The classic 150 seems to have lots of bass -for a triode amp-.

The tube saver circuit is something of a party killer, but I haven't tripped mine in a while.

One of mine had a problem once, it was a $1.50 part and ARC did a sweet job fixing it and getting me going again. Their service is a class operation! (thanks Kalvin and the gang!). It was a total of two hundred dollars, maybe less. I'm kind of a cheapskate, and i didn't mind paying. I think mine were made in 1988... That was twenty five years ago. They're entitled to a hiccup now and then. I'm keeping them.

I'm not a big fan of these amps. Check to see if the units have the old grey Mepco Filter caps in the center of the amps. If so, they must be replaced. The Classic 150 followed the M300. It's basically the same amp except the CL150 has a triode connection at the output tubes. It is Fet transistor except for the outputs making the amp ARC's first hybrid amp. The M300 was later connected triode at the outputs because of tube issues at the time. Philips/Sylvania had stopped making 6550's and the only tubes that were available at the time were awful Chinese coke bottle 6550's which failed often. The filament stayed lit but the tube would fail to conduct. The tube that followed, the Chinese KT-88, was just as bad. Since it was easier on the tube to run the 6550 pentode as a triode, the CL150 was born. M300's that were turned into CL150's have larger power and output coupling transformers. Otherwise both amps were the same.

Actually the amps in triode lowered the noise floor considerably.

Not sure about the smaller transformers, our audio club has m300s running in Triode, but I cannot see a physical difference between them.

HiFiGeek1, I know what your qualifications are and I respect you and your words and opinions completely, and I don't want to get in an argument with you...
But ARC techs tell me that the transformers are exactly the same. I live in Minneapolis, and we have really good access to ARC people.

I do, as I mentioned, respect you and your word(s) completely, and your experience. Just saying what they said to me.

You're right, they're hybrid amps. The low noise of the Fet gain stage makes them very quiet amplifiers, the noise floor is super low. In my local area, Minneapolis, they're considered one of the best kept secrets of the audio world, actually... but I have my pair, and I don't mind if the price increases. there really isn't any noise in them, they just have a tube output stage... the combination of the two sounds really good! To say that they sound like a tube amp without tube noise would be accurate, because they are, but many tube amps have little to no noise in the gain stage (this is why we replace the stock Sovteks in an amp's gain stage with NOS tubes, or a quality new production tube, or at least use the Sovteks as followers, where they do no harm to the signal...)

It's interesting that, in this particular iteration, ARC decided to go the opposite way of most amp manufacturers and make the GAIN stage FET and the OUTPUT stage tube... Usually its the other way around.

ARC tried putting the tubes in the gain stage and FETs in the output stage in its "Hybrid Drive" amplifier... And I have seen several examples sold as-is, needing repair... and several others, freshly repaired, up for sale. The amount of those on the used market, and the underwhelming prices they sell for, as well as the reviews I've read, as well as the relatively short production run of that product, indicates that it might not be a successful product... But as always, YMMV.