[Phil G4SPZ]

Avo signal generators are pretty robust, so one like that should be a good bet, better still if it can be relied upon to be working and accurate.

Colin makes a good point about the valves and the LT voltage. 1.3 volts might be a bit low. You could try running the set off batteries, which I must admit I prefer to do when repairing portables, as it eliminates the PSU as a potential source of faults as well as being safer. Just lash up ten cheap pound shop PP3s in series for the HT and a single alkaline D cell for the LT.

I can test your valves for you and I probably have some spare good valves if you need any. Drop me a PM when convenient.