Put it on a variable output isolation transformer and bring it up slowly while monitoring the plate voltage of the output tubes. Start with that. Check for excessive ripple on B+ lines.
Phono inputs in the back: 80s-> If it was from the 70s it would have had a din-connection (round plugg with 5 pins) Does it have a pre-amp for a turntable? My guess is that is a Radio/TV store had a guy in the back building these from parts collected over time and sold in store. Probably a Macintosh clone or something. Adjustments are probably for bias because when components sometimes change so do values in the design. It probably sounds better than most transistor amplifiers. I would change take out the power supply and change the capps that looks broken. If you get it to work it probably will sound awesome! Good luck
@@HiFi-DIY thanks for your message , sell to me , I really loved to fix and assembly any kind oof tubes amplifiler, like the one I build serval years ago,,,if u hav a email I can send you some photos , thanks
