Super Tube Amps waiting for mods.........
Find a pair of the Hammond organ amps with the quad of 6V6GT & pair of 6J5 tubes. These cost about $50 to $70 each on eBay.
Change one 6J5 to a Sylvania 6SN7GT 'T' type plates with a twin tail phase invertor design & use any 6P5GT (best) or Sylvania 6J5GT preamp tube to that 6SN7GT. The B+ went thru a speaker field coil magnet, thus you will need to jumper this out. Keep in mind, the audio transformers are excellent with cathode feedback windings & even have a following up to 8-watts for SET type amps. The PS is an LCLC design with an oil cap on the output. Even the pair of chokes have a low DCR.
Triode connect the 6V6GTs (15-watts output available) & make sure bias is at -25 volts thru the cathode resistors. If the B+ exceeds 350 volts, change the stock 5U4 to a 5R4 rectifier tube (Sylvania 5R4GYB are best). The best 6V6GT (never the metal tubes) are older Sylvania & believe it or not, newer GE 6V6GTA with grey oval plates.
Be prepared to hear a set on monoblocks that outperform most amps that cost over $2K or higher in cost. If not, review your mods to the amp, something is missing on your part. Remember, the amps sounds only as good as the preamp driving it.
Note: The oil/paper coupling caps are fragile, you may wish to change to inexpensive AuriCap. AuriCap take about 200 hours to reach their potential sonically.