It's been a while since posting here...
I have had this 1965 Lectrolab R600C, 6ca4 tube rectified, 2xel84, 14-ish watts for a few years, courtesy of Fleabay. She has just the right amount of janky beat up chintziness to her stain spattered sides, chewed wood corners peeling out under the tattered dirty blonde cloth covering, and slightly sexy sagging grill cloth to have some decent visual mojo on stage. She came with a Censen C12R that was working fine but got immediately yanked. The clean tone was too mid scooped and the dirty tone of the amp as opened out of the packing box with the volumes cranked up reminded me of a jar of angry crickets, unique for sure not as musical as I thought that the circuit should do. There was something in the circuit that was making the speaker sound like that, and all of it had to GO. Yep, the late 50 year old dirty blonde sleaze bag somehow still out to do her hustle is the look fo sho Mojo.
This was the second to last operation she'll have done, then I'll be finished with a long satisfying process. While I had the chassis out I noticed that one of the wood end mounting blocks had been broken loose from the cab side and had a staple leg preventing closing the gap back up. Either shipping or more likely the previous owner had a hard drop incident. Snipped of the staple and glued the block back. Then I swapped out the four remaining low quality tone caps for some really nice Russian mil spec ones at the same values. All of the originally (chosen for cheapness, screw the sound, just get the values within 20%) tone caps have now been replaced by some sort of foil and oil super top end Russky mil spec stuff, and yes, there is a huuuuuge difference in the sound going to the swapped in speaker, a 60's vintage all original University Diffusicone, which makes the original jensen of similar age sound like what it is, a cheap crappy speaker in comparison.
Now I have an amp that looks crappy but sounds very, very, boutique-y expensive. There is a real warmth to the tones with great balance from a big bottom to the pixie dust on top (Diffusicone 12 has 35-10,000 freq response) now that was not there earlier. If you ever find one of these Lectrolab R600C's, snag it. Also if you can find a Harmony H-306A they can be tweaked to sound astonishing as well. The circuit is very close to the Lectrolab's but the Harmony runs 6v6's and a 5y3, or in mine, a Bendix Red Bank 6106. They are vintage cheese amps with what looks like spaghetti true point to point wiring but these run very quiet and their bias tremolo has that unique harmonic singing thang going on in the sustain that other tremolo topologies just can't do.
Only one operation remains, I am going to go to my tech and determine the best place to break the circuit for a simple interrupt FX loop. For the first time I will drill holes in the chassis (gasp) but again, even though quite rare, this was only a cheesy amp to begin with. Not sacred. Right now the amp sounds great with the fx going into the front end but I have this Dumbulator style tube loop buffer waiting.
There us a lot more out there online to make it easier to learn about how to work on and how these old simpler smaller tube amps work than just a few years ago. These two models of vintage cheese amps mentioned are very good rabbit holes to explore. The results for me in terms of quality of sound improvement has been flabbergasting, frankly. Grab and go greatness here.