[Arran]

The neurosis over 6X5 tubes seems to have originated from Brand Z sets with crappy power supply designs. The set you mentioned used a pair of them in the power supply rather then using a 5Y4/5Y3/80 to do the same job even though that transformer had a 5 volt winding for that purpose. It was really stupid in that a 6X5 has a maximum current rating of 70 ma, to get around this they connected both diodes in each 6X5 together in parallel to make a single diode. I guess they thought this would give them the equivalent of a 140 ma rectifier, well no it didn't. To make matters worse brand Z was notorious, especially in the 1939-42 sets, for using power transformers that were barely adequate to do the job.
The Philco 42-380 used a 6X5 rectifier, the 41-280 and 40-180 often used a type 84, which is a six pin equivalent of a 6X5. Here's the difference between these and the Brand Z model, these sets used 7 tubes not 12, they also used type 41s which are a six pin equivalent of a 6K6, not 6V6s, they also only ran them at 190-195 volts on the plate and screens rather then 220 volts.
Regards
Arran