Atma-Sphere MA-1 amps

I agree with Pubul57. I used GTAs and was very pleased. When I looked to get more, Andy Bouwman at Vintage Tube Services told me there was very little difference in the sound of the GTBs up through the early '70s manufacture. That's what I'm using now in my MA-2s, and I don't notice a difference. From what I hear in the amps, I wouldn't pay a premium for GTAs over early manufacture GTBs (up to early '70s).

The GTs have a bit of special, but as Pubul57 notes, you can only use them where the high plate voltage capacity of the As and Bs is not required. I need to get a quad to try once again.
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This is a very interesting thread. Trcnetmsncom, I looked up the impedance curve of the Avalon Eidelon. It's below 5 ohms (closer most of the time to 3 ohms) between 50Hz and 20kHz, except for a narrow "peak" in the midrange, where it gets up to 7 ohms. This is not an optimal match for any OTL (like the Atma MA2) that does not use negative feedback to achieve a low output impedance. However, the MA2 has such huge power capability that you are able to overcome the impedance matching problem to a large degree. Nevertheless, I wager that if you were to interpose a pair of Paul Speltz's Zero autoformers between the amp and the speakers, the perceived unpleasant treble distortions would disappear. Given the large investment that you have already made in the amps and speakers, the Zeros amount to a trivial additional expense. I don't think one can ever talk about how an amp "sounds" without considering the speaker load.

Lewm,

Thank you! That is very interesting. In fact I wanted to research the same, but then was too busy to do so. By the way, it was the cable breaking in not the Atmas after all, when I began to seem to hear the same "thinness" through the Sound Labs, which Trcnetmscom had described hearing through the Avalons with them. Wanted to report that anyway.
Cheers,

Since we are on the topic, sort of, what are your preamps of choice with the Atma amps. I assume the Atma pre would be a natural pairing. Was that best for you? Have you preferred something else? Why? Or tried others and decided the Atma pre was best for mathcing with their amps? Why? Your thoughts?