[Penthode]

In a situation like this, there are some basic tests I like to perform. First check the voltages around the 6BQ5s. Ensure the plate, screen and control grid voltages are correct. Plate pin 7 and Screen pin 9 should be roughly the same between 200 and 250 volts. Control grid pin 2 bias should be around -8 volts.

If that is okay, inject a signal to the control grid of each 6BQ5. I like to use myself by touching a screwdriver to the control grid and listen for a faint buzz. If you are not used to doing this, you make wish to use another signal source such as capacitively couple the filament supply or a separate signal generator. A two or three volt p-p input shuld provide a noise.

Have you checked the voice coil continuity of the loudspeakers? Or tried connecting a transistor radio output to the speakers?

If the 6BQ5's are okay, then you move back. The cheap coupling capacitors to the control grid of the 6BQ5's are always suspect.