TSL 122 Repair

[musicman]

Looking for some help please
Just bought a used TSL 122 combo - serial number indicates a 2003 model with the original main pcb (can't remember the number)
Got it cheap as it has a noticable hum, particularly on the clean channel
Took the back off and it has 3 probably original Winged C EL34's and a single JJ in the outer right socket
Powered up and the inner right =C= didn't light up, jiggled it about and it did
Then tried to bias - the left hand pair bias ok (90mv) the right hand pair are up around 140 even with the bias screw turned all the way down
I've had a good look at the pcb's & can't see anything burnt or any other obvious sign of a problem
I've ordered a new matched quad of JJ's and will give the tube sockets a squirt of contact cleaner before I fit them
I've also seen a suggestion to measure the voltage between pin 5 and ground with the amp live but no tubes plugged in. I don't know what the reading should be but if all readings are about the same this is supposed to show that everything up to the bias circuit is ok
I understand this can be a common problem with the TSL
I want to try obvious things like new valves to see if this solves the problem myself but realise I may need to take it in for repair
Does anyone know any other simple tests to perform or a good amp tech near Sheffield UK please ?
Thanks

[DeanM]

you could try swapping the valves on the right hand side over to the left and see if the really high bias reading follows. if it does then thats a good indication that its those valves that are the problem.

[musicman]

Thanks DeanM,
Tried a couple of things.
Now fitted a new matched quad of JJ EL34's but the problem persists so I've taken it to an amp tech.
Pin 5 to ground measured 523v which sounds high to me.