Atmasphere amps trustable?

Back in my earlier and more adventurous days I bought a pair of Fourier Systems Panthere monoblocks, those with 8 of the Russian military triode 6C33CB tubes in each chassis.  They were based on the original Futterman design and were different than anything I tried previously or since.  They powered my Wilson Audio Sophias with an enormous soundstage and unmatched transparency, but did not have that lean, hyperdetailed, small-image sound that most other amps have.  I would characterize the images as "diffuse".  Using a pair of autoformers helped also.  However, in addition to doubling as space heaters, drawing 5 amps at idle, they were absolutely unreliable.  Sometimes one channel would go down, popping out a little male-shaped red circuit breaker in the back, while on other occasions they sounded less authorative and a check of tube fuses would show several were blown.  After investing in Buss fuse company stock I contacted Ralph Karstens and he offered to refurbish the amps but graciously suggested I clean and re-tension all of the tube sockets as they are tempered by the prodigious heat thrown off by the amp.  So I had a backyard project with the amps disassembled and parts all over my patio furniture, not to mention an exasperated spouse.  I then took it to Brooks Berdan and their technician replaced some diodes and other things I don't understand, and the amps then did become reliable.  However, the damage was done and I no longer trusted them and sold them to get something much more reliable.  I have never heard nor seen in person any Atma-Sphere equipment, but I did look into these and understand they use a different circuit called a Circlotron which is apparently more reliable, but almost certainly sounds different.  I have thought about matching these with my single-driver speakers but reluctant to do so based on previous experience.

Thanks for providing that input, Roger (Rlawry).

It wouldn’t surprise me if a contributor to the problems you had with the Panthere amps was indeed an inability to deal with the heat produced by the 6C33C tubes, which as you alluded to run extremely hot. They consume something like 40 watts per tube just to heat the filaments, and considerably more when bias currents and plate dissipations are taken into account. The 6AS7G power tubes Ralph’s designs use consume about 16 watts per tube to heat the filaments.

Also, for the record, a minor correction: The Panthere was produced by Fourier Components. Fourier Systems was a speaker company that existed during the 1980s, with Peter Aczel of "The Audio Critic" publication as its president. I’m pretty certain that there was no relation between the two companies.

Best regards,
-- Al

So OTL amps are like Ferrari: fast, powerful, maneuverable, but require very high maintenance to preserve an original condition due to excessive heat figures. 
I still prefer comfortable and low-maintenance Subaru over fast and powerful Ferrari.

 I have thought about matching these with my single-driver speakers but reluctant to do so based on previous experience.

If you are going to run a lower-powered speaker like a Lowther, its in your best interest to install a speaker protection fuse in the circuit if you plan to use any amplifier that can make way more power than the speaker can handle! That would include most of our amps.

In a nutshell, we would not be in business for 40 years (so far) if our amplifiers damaged speakers! But common sense should always be applied when matching audio gear.

Power tubes can blow though, and I don’t know how well protected Ralph’s amps are if this happens or what kind of warranty Ralph offers.

In the old days we put way too many fuses on the amps as we were concerned about the effects of tube failure. As time went by we got the number down to 3. The fuse by the power cord blows if the amp tries to make too much power, and this has proven very effective for speaker protection since we started using this system, which was about 25 years ago or so. The amps are warranted 3 years (although we are not particularly picky about that and the warranty is transferable) and tubes are warranted for 1 year.