it is possible that it is a tube causing the problem, but it maybe that a winding in the oscillator or tuning coil for SW has a bad solder joint, or maybe even a mica cap in the tuned and oscillator circuits has actually failed, but sometimes there is a paper cap of small value, and those are always suspect.
In any event, the problem seems to be localized to just the RF and oscillator section, as the remaining stages are shared between the AM and SW.
But getting back to the tube you mention, is it a noisy tube to start with? Is it microphonic?
Also- is the station you are tuned to actually operating with an AM signal, or are you tuned to a military or Ham station that is transmitting sideband?
:I have a Philco and have been trying to figure out for a few days now what is causing the short wave to be distorted. AM is fine loud and clear. It seems that the stations are there, I have looked it over top to bottom. Other than B+ is higher than it indicates on the schematic I cannot find anything wrong. I have no tubes to swap as I have no extra of some of the 7C* series. Could it be a tube?