The 6J5 vs 6C5

[k4kyv]

I had always wondered why these two types of tubes existed, with such similar characteristics.  Apparently the 6C5 came first, and the 6J5 is an improved version.

From a European Sylvania tube application data sheet:

...In general, the applications and operating conditions are similar to those of tubes like the 76, 37, 6C5 and 6C5G...

Although the 6J5 and 6J5G have the same amplification factor as the 6C5 and 6C5G, the mutual conductance has been increased, with a consequential reduction in plate resistance.  The output capacitance of the 6J5 is about a third that of the 6C5, and the design of the tube is such that the 6J5G is especially adapted to function in equipment at very high frequencies.

[WU2D]

Don,

That is a VHF tube - Hi...

When I was a freshman in high school I built the basic super-regen circuit out of the 1958 ARRL handbook which was just a triode and I simply used the venerable 6J5 because I did not know any better. It was a triode - good enough.  Believe it or not the thing worked slick as high as the 2M band and it even did a good job with aircraft AM and even Broadcast FM. It put out quite a bit of RFI!

Later I did a tighter construction job with a hot 6BZ7 with half of it as an untuned RF amplifier for isolation. That one was hot and worked up to 450 MHz no problem. 

Mike WU2D