6L6GC

[RightLurker]

A friend recently dropped off a Fender Bandmaster Reverb head for a checkup. All of the tubes are RCAs. The power tubes are 6L6GCs, both RCA, but one is taller than the other. The taller of the two has a small "FK" printed on the bottle; the shorter one has a small "CT." The internal construction appears similar, if not identical. Can anyone educate me on the differences between the two tubes? Thanks in advance.

[sluckey]

I's say about a half inch.

[pompeiisneaks]

aside from sluckey's sarcasm ;D, I think the internal components look identical in size etc, so maybe they used up some glass from older larger ones on some of the newer internals. Just a guess. I know over time they found ways of making them slightly smaller etc. and may have just been using up the old glass with the new internal sized components.

Just an educated guess.

~Phil

[sluckey]

FK and CT were the initials of the glass blowers. FK worked the mid shift and was known to blow a bit harder. His glass became known as 6L6GC. CT's short stuff was split off and became known as 5881s and awarded a huge government contract. I learnt that from Alfred A. Newman.

[xtian]

Thus, the origin of the term, "blowhard."

[Ten Over]

I learnt that from Alfred A. Newman.

Any relation to Alfred E. Newman?

[Ten Over]

Thus, the origin of the term, "blowhard."

It just goes to show that you can learn something new everyday, no matter how old you are. I always thought that term came from a Geisha Girl's mangled English.

[martin manning]

Same tube from different production runs before and after a height spec change. Most likely a cost-cutting move.

[Stevem]

The bigger tube is just a later blackplate version, the internals are the same .

The smaller tube likely has a tighter vacuum level

[sluckey]

I learnt that from Alfred A. Newman.

Any relation to Alfred E. Newman?

Yes. His twin sister. I get'em mixed up all the time.