Atma Sphere

I have M60 II.2's and use only half of the output tubes since 30 Wpc is okay for me. Not much heat--no problem with the amps sitting behind the speakers a fair distance away from the listening area. Of course there would be more heat with all eight output tubes. You have to balance them and adjust bias once in a while, and need a multimeter ideally since the built-in meter is said to be poor, and that's probably beyond the capabilities, and also not to the liking, of a nonaudiophile. But hey, that isn't you, is it? After all, you posted this query on Audiogon.

The Atma-Sphere amplifiers are totally stable and absolutely reliable. The output tubes are very rugged tubes and will run for a long, long time. When replacement time does come, they are not terribly expensive and they do not have to be matched. A-S sells them at very reasonable price.

The bias on the amps remains very stable, in my experience. Over the first 30-days, you will need to monitor/adjust it every few days, but once it settles in, it will stay very stable.

All of the Atma-Sphere amps operate in Class A. Any output device run in Class A, solid-state or tube, throws off a fair amount of heat. How much heat depends on which model amp you're talking about due to the varying number of output tubes. The M-60s are modest heat producers compared to the MA-2s. The MA-2s, which I own, will definitely warm up a room.

I agree with the recommendation to visit the Atma-Sphere Owner's Group web site, www.otlamp.com The folks who post there would be happy to answer other questions you may have.

Depending on which amp, i.e. the larger number of output tubes used, the hotter the amp runs. I have the MA-2's which consists of twenty 12AS7's per mono-block. Hot, at times, is an understatement. I live in Wisconsin, so a good portion of the year temperature is a non-factor. The only other A-S amps I have heard are the MA-1's. Fewer tubes, less power, less heat.

Regarding tube replacement, the drive tubes, 6SN7's have a reputation as long running, consistent sounding and reliable; especially NOS. The outputs....not so long, but not all that expensive.

My amps, nor the other two I have personal experience with have ever had reliability issues. Do take Scifi's suggestion and research either ASOG or threads on Audio Asylum.

The amps are very impressive. Well worth investigating.

Hello Josef,

The Atma-Sphere amps do generate more heat than most amps, comparable to any Class A amp of a similar power rating. The big MA-2's dissipate 800 watts per chassis (idle; a bit less when playing loud), so a pair of them are like having a 1600 watt space heater running wide open. Down in my homeland (Louisiana), that's really too much heat to be practical.

As you can see from Tom's post, you can use less than a full complement of output tubes (assuming that works with your speakers). And of course the lower wattage models don't put out the heat that the big ones do.

Occasionally a tube goes bad, but in my experience no moreso than in a push-pull tube amp. The only time I've ever had a tube failure is when I made a mistake and biased the tubes too high. Ralph warns that setting the bias too high will shorten tube life, and might I add, spectularly so! Flash/pop tinkle. But there was no damage to the amplifier; I popped in new tubes, corrected the bias, and haven't had any problems since.

What speakers were you considering driving with Atma-Spheres, and which model amp were you looking at?

Best of luck to you,

Duke

Thank you all for the good advice. I found all the responses very helpful and informative. I wish you all a prosperous and happy new year. Thanks again.