Zenith 6L6GC manufacturer?

[gary sanders]

RCA or GE?

[Phil_S]

I'm liking it for a Sylvania based on the codes on the base and style of writing "6L6" on the glass. I don't know diddly about the internals.

[gary sanders]

yeah the stamp on the glass kind of veered me away from thinking it was RCA.I love the "replace with GENUINE "Zenith" Tubes".kinda funny

[rooster]

This can typically be marked as Sylvania and many others but I believe it was built by Philips. This is an STR XXX tube. This looks like a single getter version and, fwiw, the double getter versions are considered the better version

[rdjones]

That's definitely a US made Sylvania.
I'm pretty sure that Zenith was out of the tube-type circuit business by the time Philips bought into GTE/Sylvania, which was in the early '80s.
In any case they were good tubes, comparable to RCA and GE.

rd