Eric Strasen
Forum Participant

Hello Bob,
Actually, the Zenith with the biggest (but not the only) 6X5 problem was their 10-tube console, which used two rectifiers. Invariably, one rectifier would warm up and begin operating quicker than the second and briefly would carry the full supply load for the radio.
Cathode to heater leakage was the result, cooking the power transformer’s B+ winding. Apparently this happened often enough during a set’s brief warranty period that Zenith was forced to send dealers replacement transformers with an added 5-volt winding.
This additional expense must have kept Commander McDonald awake at nights.
Nevertheless, the company continued to use 6X5G’s in new production sets through at least the 1942 model year.
Your 5-tuber should be quite safe with a 1960’s production 6X5GT.
But as I have said before and will say again, I wouldn’t put a 6X5G in ANYTHING. Why take the chance?
The GT’s are widely available and are not expensive.
NOTE: Although there are a number of Zenith detractors, and even haters, around the web, I am not one of them. I have gobs of their sets and generally am pleased with their design and construction.
I just don’t understand why they stubbornly stuck with the 6X5 as long as they did.
I will close this out with some pictures of my 7S633.
Happy New Year,