Amps Atma-Sphere M-60 Mono blocks OTL design

Hi Bob (rfogel8),
It’s good to see your post and I’m glad to know you and your family are doing well, life is precious. I can’t say that I am up until 4 am but I still listen to music pretty much the same as always. Roughly 3 to 4 hours (sometimes longer) 4 or 5 days a week.

I still very fondly recall my SET amplifier with your easily driven DIY speakers and your MP-1 preamplifier, it was really a fun and memorable evening, natural, engaging and relaxed. Wow, the years fly by 😊. I am happy that you are finding the time to enjoy your wonderful system. Music is good stuff to spend time with and appreciating its charms. 
Charles

I notice with concern, the MP-1 now uses only two 6SN7's per side instead of five. Hopefully we're not losing any of the good things valves bring to the table. Besides lower noise, what's your thinking Ralph? Cheaper to re-tube? Just kidding! Hey, what about tube rolling? Have all my NOS jewels suddenly become worthless?

Ha! Actually the MP-1 uses three 6SN7s per channel. In the Mk3.3 version, prior to its release we had spent two years working on a Constant Current Source (CCS) circuit that could outperform the one in the earlier preamps (and amps). In the amps the old CCS drifted about 17 parts per million over an AC input voltage range from 100V to 126V. This in turn assured that the voltage amplifier performance stayed the same over the same range. In the preamp the same circuit was used but the preamp has severely regulated supplies so it was a bit more immune. At any rate, the new CCS is performing at about an order of magnitude greater performance so we were able to improve the differential effect in the voltage amplifiers of the amps and preamps; in the case of the MP-1 this meant that two 6SN7s got eliminated in each channel as they were CCS circuits. But the actual signal path tubes are the same.

To remove the bulb on one of our amps: unscrew the lens (lenses of other colors and texture are available). The bulb is an old-school bayonet mount and so you push on it and twist it 90 degrees counterclockwise and it pops out of the holder. To reinstall is the reverse process. The stock bulb is a type 47 which is a 6V lamp (we run it at 4.5V for greatly extended life and to dim it a bit); a 12V lamp can be installed.

Ralph, I stand corrected. I saw a photo of the MP-1 3.3 on "What's Best Forum" and as the saying goes, sometimes we look but don't see. Three 6SN7's and five 12AT7's per side. As usual, the layout looks meticulous.

I assume the front 6SN7 nearest the faceplate still has the most effect when tube rolling? 

Glad you're doing well Charles and still listening regularly. I see Fremer was in town recently and spent some listening time at Jeff's. We should get together soon and spin some tunes. You still running all Coincident? I thoroughly enjoyed that evening listening to your Frankenstein's. At only 8 watts and as loud as I cranked them up at times, I couldn't believe they never clipped. I see why 300b's have such a loyal following. I'd love to hear what Blume could do with 845 monos. I wouldn't give up my MA-1's but variety is the spice......