[Techman]

Exactly - that's what I should have added in the previous post. Connect it to an external power supply with crock clips to the heater pins, or as you say, do the same from the heater winding of the transformer.

Just to add for clarity - No HT, just lay the valve on the bench and crock clip to the heater pins from a suitable power source and look for the heater glowing.

It's all about logical thinking. If something isn't working as expected, don't just jump in and blame the most obvious part. Take a step back and try to focus your mind and start to logically think of all the other possible causes of the fault. It may seem absolutely ridiculous that there could be no connection from the valve base sockets on the chassis to the valve base pins on the valve, especially as you've cleaned them thoroughly, but these type of faults are more common than you think - always expect the unexpected when faultfinding an old radio.