In the August, 2007 issue of Tube Collector, a publication of the Tube Collectors Association, is an article, "History of Development of Vacuum Tubes and Vacuum Tube Sockets," which contains this clip describing a temperature problem with the CW-933 tubes when used in submarine chasers:
Trouble with Insulating Wax Melting on CW-933 Vacuum Tube
The CW-933 tube proved to be satisfactory in service from an electrical standpoint. Some trouble however was experienced with the insulating wax in the base, melting and flowing over the contact points when the tubes were used under excessive temperature conditions prevailing in submarine chasers.
This trouble was quite serious and was called to our attention for correction. The insulating wax in the tubes which gave trouble was known as "Zinsser's regular insulating wax," the flow point of which is below 160° F.
We were informed, however, by the Navy that the atmospheric temperatures in chasers sometimes went as high as 225° F and that this high temperature condition was apt to be aggravated by carelessness on the part of the operator in not cutting off the filament current to the tube when the sets were not in operation. Investigations were started at once with a view to obtaining an insulating compound with a flow point above the maximum temperature likely to reach in service.
Our Chemical Laboratory developed a sarco residue compound which met the temperature requirements satisfactorily, and at the same time a compound was developed by the Manufacturing Department which, altho its flow point was a few degrees lower than our sarco residue compound, was finally approved , although it was felt that the only certain way of preventing trouble with the flowing of the wax was by doing away with the use of wax altogether and adopting a style of base similar to that used on the VT-2 vacuum tube. Investigations along this line were suspended, however, at the cessation of hostilities.
The chaser radio room was next to the officers' quarters, which was separated from the engine room by a steel bulkhead -- but with so many penetrations for pipes, wiring, etc. that there are many notes of exhaust filling the quarters. This plus the heat generated by running the equipment and the generally poor ventilation, combined with service in warm climates, led to these cases of excessive temperature.