[R-390] R-390A 6C4 Mixers

[Byron Tatum]

Hello-    If any members have the time I wanted to ask some questions regarding the 6C4 tubes used as mixers in the R-390A.    I have been going through my 6C4 type tube stock here, testing them on a TV-7D/U, preparing for some work on a few receivers.    Is there any advantage in using the variants of the 6C4, such as the 6C4WA, 6100 or 6135 instead of using the plain 6C4? Can someone explain the differences between these variants and the common 6C4. As I understand it the -WA, 6100 and 6135 variants mostly differ in ruggedness and possibly quality of construction. Just curious about other's opinions here. I have researched these variants and studied the data sheets. Was wanting to know if any electrical properties of variants would benefit mixer service.    I know that sometimes the particular brand/variant of 6C4 can be critical in oscillator service. I experienced this some in restoring a few HQ-180 receivers and picking out the most stable 6C4 oscillator tubes.    Thanks for comments,Byron W5FH