I’ve pick these amplifiers from local second hand repository for a long time ago.
They’ve used in the theater somewhere before.
Output impedance are 200 ohm and 166 ohm,
so need line matching transformer for use with standard speaker too.
Nippon Electric “2154-H” 50 Watt Mono-Block Power Amplifier
using 807 tubes in Push-Pull configuration
drive by 6AU6 with separate rectifier for driving stage and power stage.
Many functions for check and test parameters. All components made in Japan.
Parts like capacitors, plastic knobs and wires seem deteriorate.
Connection points so dirty and iron parts had corrosion.
No any information about this on WWW.
Difficult to draw schematic for refurbish.

So ………… it’s time to clean & change circuit with new parts and tubes.

Which tube should I go with?