Compact ~20WPC Tube Amp

@aricaudio 

With most SETs the driver is the amplifier’s downfall- not the power rating of the amp, or the 300B.

Aric this is precisely what the builder of my Coincident SET (And speakers) explained years ago. The main limitation with some SET amplifiers is the choice of weak/inadequate driver tube. Just as you say, this driver needs to be robust. The DHT output tube demands this. He chose the 6EM7 rather than the 6SN7 for that reason.

@atmasphere 

Good advice you gave to Israel Blume (Coincident). I’m happy that he took note of that wise counsel,😊

As you’ve pointed out before, higher speaker impedance means less amplifier stress/work and less distortion.

Charles

@charles1dad Exactly! The 6EM7 has two different triodes inside, one has high gain and low Gm so is used aptly as a voltage amp where its only job is to make the input signal larger, which is then cap-coupled to the higher Gm, lower gain and lower output impedance section of the tube. Then that is coupled to the 300Bs grid by a 2:1 interstage transformer so it makes a dog's lunch out of the 300Bs grid current and allows the amplifier to realize the full power of the 300B. My 300B is similar, but takes a slightly different road to get there (same principle however). 

Regarding speakers, another trick is to use an output transformer with a higher primary impedance to drive a lower impedance speaker. I've built amplifiers for several customers where their speaker's impedance profile dipped down heavily into 2 ohms, and the SET was able to drive them just fine, or more so surprisingly fine!

All the best, Aric

compact ________?

We really know what we own or have known,

My Cayin AT88 is not compact, a ’regular’ sized tube amp, 45 wpc. It had to sound as good as my Fisher 80az mono blocks made in 1958, it does, and gave me remote volume, which allowed me to use a vintage tube preamp with no remote anything.

If interested, get a later model with external bias, I needed 16 ohm taps, only m1 has those. later have 4ohm and 8 ohm taps

https://www.google.com/search?q=cayin+at88&rlz=1C1CHBF_enUS949US949&oq=cayin+at88&aqs=chrome..69i57j0i22i30l2.14365j0j7&sourceid=chrome&ie=UTF-8

6 moons review convinced me to try it, glad I did

https://6moons.com/audioreviews/cayin/a88t.html

Regarding 'compact', the Cayin CS 55A has inbuilt phono and USB inputs, half size width and puts out 22 Watts in Triode (40 Watts in ultra linear). So lower your box count and get great amp for less than $3000. 

I will have to throw a few votes in there for the "talk to Aric" comment.

Ive spent the last hour after getting home from work. Listening to a nice mix of mellow male and female vocal/jazz. Playing my Innuos Zen thru a Pontus II To a Aric Audio 6sn7 preamp (currently running Linlai tubes) and Aric Audio Super KT88/120 SET amplifier (currently running Westinghouse 6sn7gtb tall bottles and KT170's in triode). At the end of the line I have a pair of Spatial M3TM's that you would never know were even in the room! Arics pieces are just amazing you should  honestly reach out to him. I don't disagree with previous recommendations as I have no experience with most. 

I do know that my experience with Aric is nothing short of amazing, a good honest man!

J.F.