어이구 복잡.. 띵..

그리고 약간의 튜닝 포인트

It is a very-very-good amp as-is. It is low-power, not low-quality.

Clean the contacts and sockets, check the tubes for faults. If they sound fine, they probably are healthy. (By the way, nothing wrong with most 40 year old tubes, and they may be better-made than the ones knocked-out in the 1980s or 1990s. My 1968 PAS2 still has all original tubes. My over-worked Dyna Mk VI from 1975 has one bad tube.)

The power supply cap and rectifier may not live forever. I'm mildly surprised the main power cap didn't go "bang" at switch-on. For "fun" use, I'd use it until it failed, then fix it. For serious use, I'd get a handful of 100µFd 300V caps and a terminal-strip, yank the can and re-cap it. I just don't know about that rectifier, but if it fails a 1000V 1A bridge is an easy cheap replacement. Be sure the line-fuse is the correct size (if it has no line-fuse, I'd use 0.5A at 120VAC or 0.25A at 230VAC wall power) so if a cap or rectifier shorts, the precious power transformer does not go up in smoke.

The tone controls are a matter of taste. I would keep them, because it is authentic. However while the output stage is probably ruler-flat, the tone control stage may not be. You could bypass it: the combination of B1a and tone-circuits has only a small voltage gain. You could strap the volume pot wiper to the top of the balance control, with tone-circuit disconnected from balance pot, and still have good gain. But on a printed circuit board, that ain't easy. And I hate to see an oldie cut-up like that.

The rest of the amp is about as perfect as a 2-watter can get, assuming you like small-feedback SE Pentode. C12 might be upgraded to 100µFd 16V. If you touch any of the other caps, do not change their values without expert advice: they look like they were sized to control feedback stability. The resistors look like good-quality jobs and I would not touch them.

If you want less gain and less distortion, try R23=680Ω. But it may squeal or motorboat.

If you want more gain and honest tube distortion, try R23=10K. But speaker damping will be very poor.

If you want to try SE Triode, find the end of R22 that is not connected to the tube, lift it, and swing it over to connect to B2 pin 5 (plate). Power will be half, damping will be OK (though hardly up to modern expectations). Gain may be low, try R23=10K.