Maybe Leaving SET for Solid State because I want bass

@atmasphere 

"That would be a lot (most) of SET products!"

Probably all.

"That’s a lot more than just 1% which is an arbitrary value."

I wouldn't call it arbitrary, It's a standard. What is arbitrary is how tube amplifier manufacturers publish specifications which provide no valuable information to the consumer to compare one manufacture's product to another. They don't follow FCC guidelines but seem to get a pass because when they were initially instituted in 1974 the market had almost completely moved over to solid state and as long as a manufacturer used the RMS method of publishing their specs (solid state) regardless of what bandwidth they specified would be in compliance with the rule. Some continued to publish completely erroneous power output, distortion and noise numbers while others strictly adhered to the rule.

Interesting the review of your M-60 mono blocks by Charles Hansen from Glass Audio in 1998 confirmed, even relaxing the tolerance to 3% as he states - "The generally accepted practice for OTL and single-ended (SE) tube amps is to use 3% THD+N as the clipping point. This occurred at 23W into 8Ω and only 9.5W into 4Ω.
Maximum output power into 8Ω was 65W (5.6% THD+N) when the B+ fuse blew. The fuse blew again during the 4 ΩΩ test at 44W (8.8% THD+N). The AC line voltage was 118V AC, rather than the 120V AC at which the amplifier is rated, for 60W (8Ω) and 45W (4Ω)."

Relaxing the criteria to 3% he could not confirm your power output specification @ 1Khz. Further he had to relax the parameters to 5.36% at 8 ohms and 8.8% at 4 ohms @1Khz to achieve your rated power of 60 watts and 45 watts respectively which leads me to conclude that from 20Hz to 20Khz using 1% as a threshold your amps like any other tube amp on the market regardless of topology can only produce a small handful of watts at best. Let me qualify that saying that there are amps that use two or more parallel A-B pairs to be able to generate a few tens of watts at best with huge amounts of AC current draw and corresponding amounts of heat. You also have to consider the reliability issues with keeping all those tubes within several percent of each tube's bias.  

With your amps you have DC offset to deal with which is equally injurious to speaker voice coils as oscillation is and they use lots of tubes together in an effort to lower output impedance which are not common in the general market, that run hot and probably has a long-term effect on reliability.

Let me say any tube amp connected to an appropriately efficient speaker with a favorable EDPR and operated within it's actual power envelope (a few watts) will have a wide bandwidth, low distortion and a clean, fast and convincing presentation.

Interesting though I wasn't able to uncover any objective test bench evaluations of your OTL amps published since 1998. Only the subjective ones from publications that don't routinely do them.

OP

look into the AGD duet power amps

AGD The Audion MKIII › AGD Productions 

I heard this driving a large floor stander in a recent audio show and man, does it move and control those large 15 inchers. 

GAN based amplification is breaking into high end audio gear and They are proving their worth and equaling the playing field. to be fair, listen to it first.  if one needs lots of power and still has the harmonics of a tube "like" tone, then look into GAN based amps

Tough question. The main problem with bass with tube amps, push/pull and especially SET is their high output impedance. Low output impedance helps control woofers. And the problem with output impedance is the output transformer. The tube amps I know that had relatively low output impedance(3 to 4 times lower than most tube amps) were made a couple of decades ago by a company called Melos. I saw the Stereophile unpublished bass response into a simulated speaker and it was almost undistinguishable from a solid state amp.

Other plusses for the amps are high power. The stereo amps are conservatively rated at 200 watts Triode and the monoblocks 400 watts. They are rich class AB. The monoblocks were25 watts class A before going into AB so your speakers would be class A almost all the time. The problems would be working on them. They are old. Schematics don't exist although a good tech can follow the circuit. Almost unknown now they should be cheap meaning you can put money into restoration. I also recall an SET Melos rated at 70 watts but I suspect they are super rare

This is just a thought by the way with some risk but with possible exceptional results.

Viva Audio out of Italy makes fantastic SET gear and has a lot of low end punch. I have heard the Viva Solista Integrated and the Viva Solista Stereo   Most recently it was the Viva Solista stereo at the Capitol Audiofest 2025 

https://stereonet.com/reviews/viva-audio-solista-mkiii-integrated-amplifier-review?fbclid=IwZnRzaAPrXzJleHRuA2FlbQIxMQBzcnRjBmFwcF9pZAo2NjI4NTY4Mzc5AAEepWyLWNYAS3Jm2D0ia62j6B4iRr4D-7fV8okUMGr3IKaJc9lPrjcbXISql8g_aem__I-Gic_jNbYVMyVSbWmSPA

https://positive-feedback.com/show-reports/capital-audiofest-2025-2/12/?fbclid=IwZnRzaAPrX3xleHRuA2FlbQIxMQBzcnRjBmFwcF9pZAo2NjI4NTY4Mzc5AAEekqBoMvFprfooMvsW1SEnFyZCIY4o5kqSQDntwf85FS6ZoleT_oHCuNt0dfE_aem_xFyuGHkJ5K3G1GyWhTLO0Q

https://www.enjoythemusic.com/Capital_Audiofest_2025/Becker/CAF_2025_Show_Report_Part_2/page5.htm?fbclid=IwZnRzaAPrX6BleHRuA2FlbQIxMQBzcnRjBmFwcF9pZAo2NjI4NTY4Mzc5AAEetbpyV4RCFKA0SVSM544w4ftXQYbRC1StKA3H1ghP32ORHkEAXX9YORbLSbU_aem_tTfwQhmXYGFEjukRyA3yxw

Interesting discussion, especially concerning SET circuit design. I will only add that in my experience: (1) solid state will offer better lows (and highs) than a comparable tube amp, but, and it is a big but, your recordings will not sound the same. Jimi Hendricks and Stevie Ray Vaughan do not sound the same with solid state amplification; it is as if they are playing different instruments.

(2) Integating subwoofers into a stereo system is a non-trivial task. Several persons have given good advice on resolving this dilemma, but much like room acoustics, there is not one solution which fits all cases, just various methods and means to achieve a common goal, in my opinion.