[Arran]

Test your tubes for heater to cathode short circuits as well, if you don't have a tester try substituting one tube for another. I'm betting that the problem is likely an incorrect negative connection on a filter cap, it's a very common mistake. Many people wrongly assume that the B- connection is always to the chassis, but 1930s era radios ( and some 1940s era ones) often used a fixed bias supply with large wire wound resistors, so the chassis is slightly less negative then the center tap of the power transformer. Another mistake that people often make is that they assume that the field coil of the loudspeaker is always in the B+ circuitry, sometimes it's in the B- circuitry, but it does still act as a filter choke regardless of where it is connected.
Regards
Arran