It appears to be a power amp issue.

Just remember that big power tubes can get VERY heavy, just pull one out when it's hot and try to hold it in one hand, I bet you can't hold it for too long.
But everyone has to learn that certain things are hot the hard way, I am constantly reminding myself that the soldering iron is too heavy to hold on the pointy end. (The hard way)

The guys here can help you get it running.  I would ask if you have tried it out yet but it seems like you know it has a problem..what did the seller say about it was it listed for parts or something? 

I would say plug it in and try it but I would hate to see it burn up some impossible to find outputs or something.

T4 E to B  0.3V

T1 E 0.6v
   B 0v
   C -35.8v

T2 E 0.6V
   B 15.1v
   C -36.5v

R5 671 ohms

D1 checks good

So looks like T1 is bad?

Is there anyone in the south west of the UK who would like to look the amp over? It may not have much wrong with it at all. Small funds are available.

Quote from: Bandito on April 06, 2024, 04:15:56 PMWould this one work? https://www.hotroxuk.com/accutronics-blue-reverb-amc2bf3.html

That is too low input impedance.  If you want to go with that miniature type, use the AMC2EF2.  In my experience, the miniature type do not sound very good.
If there is not enough room for a 17" tank you can get a 9" type.  For MOD or Accutronics brand, 4EB2C1B is 17", 8EB2C1B or 9EB2c1B are 9" long types.
You may find them for less money at other UK sellers, like Watford valves, etc.

Quote from: g1 on April 05, 2024, 02:03:37 PMShows 600 ohm impedance for the tank so 4EB2C1B tank should work.

Would this one work? https://www.hotroxuk.com/accutronics-blue-reverb-amc2bf3.html

Thanks for your comments! Do you reckon this to be a good amp, worthy of resurrection?

Sometimes the removal and re-install of tubes will clean up (deoxidize) the sockets.  Maybe that got it working.

Depending on the droning sound, it could be a microphonic tube.  Try tapping them gently one at a time, or holding them with a rag or something to damp the vibration but keep from getting burned.  Generally, microphonic preamp tubes will be higher pitched whistling or squealing, where power tubes will more likely rattle or make low pitched rumbling sounds.

The E to B voltage of T4 (0.3V) seems to not be enough to turn it on.  Maybe checking directly with probes at E and B will give a more accurate reading than checking voltage to ground.
The voltage to turn it on should be developed across R5.  That is created because of current through T1.  What are E,B,C voltages for T1 and T2 ?