Recommended Speaker List for Atma-Sphere OTL Amplifiers.

I’ve bought the M60s. It’s a rather different step then I was originally going to go but the opportunity to have some truly excellent amps was hard to pass by. I’m not a rich man being a retired military career man. I had originally got out of 300b amps they just didn’t do it for me that little power. I was going to play with vintage for a bit until I decided where I was going. The Atmos amps sort of fell into my lap so it’s changed my path somewhat.  
I only brought up the Freya as I thought it was a fully balanced peramp that could be a starting point. But I do have a totally rebuilt vintage Sansui CA 2000 I was planing for a vintage set up that’s actually quite good sounding but only single ended.

Obviously it’s a vintage preamp and not to the level of Ralph’s own preamps. But after spending money I didn’t really have on amps I’m not in a position right now to buy a preamp until I sell off the vintage gear I have. And let’s be honest my speakers are not going to show what they are capable of anyway at this point until I upgrade. 
Thanks for the advice my friends. Looks like my audio journey has taken a turn for the better.  I’ll be picking up the amps in a week or two once my friend reopens his shop.  Closed for cov19 at the moment.  From there I’ll buy a new tube set as they are questionable and mismatched brands. Actually any recommendations for tubes for that work well in the Atmos OTL would be helpful. 
Ralph thanks for the support. I believe these amps were sent to you in 2015 for the mark 3 update. I’ll check once I get them and if not arrange to have them sent to you. I can see one amps serial number in my picture it’s 236 I can’t make out the other amps. 
Exciting times in audio. 
Cheers my friends 

Glen  Newdick 

I’m sure you will enjoy the amps Glen, I believe you could use the Sansui with no issues except you will need to short pins 1 & 3 per the Atma manual (see below)
"If you use the RCA input connector, make sure a shorting jumper is installed between pins 1 & 3 on the XLR connector else a buzz may result"
The most important tubes for the sound are the driver tubes the 6SN7’s, I know you are not buying stock but the stock tubes that comes with the Atmas out of the box usually chinese Shuguang Brown Base 6SN7s are very decent, that said you could improve with NOS tubes or even some Chinese Boutique tubes, if you need more on the subject I can provide more details and I’m sure others will do as well.The power tubes "sonically" won’t provide much, not many options either, the Russian 6AS7G Svetlana’s 6H13C are very very stable, sound is magnificent and to me these are the tubes to go on this amps as far as power tubes is concerned. The NOS RCA’s 6AS7G could provide a little more power at the expense of reliability and headaches, and money too. I went that route and turned back, my MA-1’s do fine with the power offered by the Russian power tube the way Ralph designed it. If you need more details I will be happy to provide such but my advise if your speakers do fine with the Russian tubes don’t change them, I experience one of the RCA tubes heavy arcing, smoke came out of the amp (or tube) and it is very common with these tubes, IMO reliability is an issue. DO NOT USE 6AS7GA on that amp, the tube IS NOT COMPATIBLE, stay away from GE’s 6AS7G, you will run into problems.Let us know what tubes comes with the amp and I’m sure Ralph or someone else or myself will be able to help.Maybe I missed it but your speakers are sensitivity? and nominal impedance?

I would not suggest using any old stock U.S. made 6AS7Gs in Ralph's OTLs. 

Just for education purposes when you say it doesn’t support the standard do you mean "it is not differential", aka duplicate stages + and -?

No- the balanced standard requires that the output not reference ground and otherwise is able to drive a low impedance. That is how cable immunity occurs- otherwise you’d have to pick your cables to get things to sound right and longer cables are out of the question.


Glen, if updated in 2015 then its a Mk 3.2 or possibly early Mk3.3; either way a good find! The plate on the front states the amp’s actual identity; the number after the dot is stamped in so will be a 2 or 3.

Thanks Ralph