Greetings from Berlin,
yes the ATM2 is maybe one of the best KT88 amps in HiFi history.
If one thinks of MC 275 - this is not completely wrong.....
The ATM2 has, in difference to modern MC 275, still, as it was on the vintage MC 275, the 12BH7 driver tube for the KT88.
The output transformers are within the best you can get, they are produced for Air Tight from Tamura - fantastic quality!!!!
If you want to hear what this amp is capable of - you have to throw out every single tube, which comes with the amp.
Change them to top of the line NOS tubes.
I use for my ATM2 a quad of GEC KT88 black plates triple getter - in my case CV 5220 from 1967.
The 12AX7 position is in my case fitted with Telefunken ECC83 smooth plates, the splitter stage is fitted with Mullard CV 493 long plates square getter coin base.
This is one of maybe 4 or 5 settings, wich blows the socks of - no comparison to the stock EH and chinese KT88 setting.
Also important is to keep in mind a valid preamp - the ATM2 - as all Air Tight classic amps (ATM1S, ATM2, ATM3Mono, ATM4, ATM300, ATM211) need the 600 ohm standard preamp - or even less output impedance.
It is a little bit as with shindo - use with the ATM2 one of the classic preamps from Air Tight, and it will fit perfectly.
Keep in mind, that the reference preamps are not made with these classic amps in mind - they all have a too high output impedance.
Perfect for the ATM2 ist the ATC1 HQ, ATC2 HQ or ATC3 HQ - ATC2 and ATC3 are just line preamps, ATC1 HQ is a full function pre, which is a modern interpretation of the classic Marantz 7C.
The ATC2 has a very compareable layout as the line stage in a MAC C20 - it uses a tube rectifier a 6X4 or their derivates - and the ATC2 can be upgraded with the matching RIAA stage ATE1 - which makes a fantastic combination.
The ATC3 is a stripped down version of the ATC2 - and inspite of the simpler layout, it sounds fantastic.
Also there is the ATE 2005 RIAA stage in the Air Tight portfolio - it is the only RIAA stage in the portfolio, which has 2 mm inputs as also a mc input - no other Air Tight RIAA shares this.
So you do not need a Step Up - but you could
)))
The ATE 2005 is a reference like RIAA stage, which fits also in the classic Amp portfolio - it has also an output impedance of 600 ohms, and it is also able to drive one of the amplifiers direct - without a line stage in between.
Hope this helps
greetings
Ekki