A few mystery tubes... What do I have here?

GilmourD

GilmourD

Eater of Worlds
Staff member
These were pulled out of a Gibson GA-55.


The single power tube that was in it (should be a pair, obviously, but somebody has or broke the other one...):

mysterytube1.jpg

mysterytube2.jpg

mysterytube3.jpg

mysterytube4.jpg

mysterytube5.jpg


Then a bunch of 6EU7's (which I understand are a low-noise 12AX7 with a different pinout):

6eu7-1.jpg

6eu7-2.jpg

6eu7-3.jpg


And a Chinese 12AU7 labeled as I've never seen one labeled before:

12au7-1.jpg
 
No idea on the power tube but I'm guessing the 6eu7's are RCA. Definitely US made and the orangish silk screen is the same color RCA used.
The "National" labeled one is probably a re-label (I'm guessing). I have a "National" made by Ei out of Yugoslavia. If memory serves they used the actual telefunken tooling to make their tubes.
Yours probably is Chinese made and sold to "National" hence the label.

Disclaimer: this is all just my best guess on these tubes. Someone else may know exactly what you've got.
 
No idea.

I have an old Gibson tube amp that had some weird tubes in it. It's in my basement and I've forgotten what they were. I seem to remember finding multiple schematics for it and having to compare the circuit to several schematics to find the right one. I think Gibson played fast and loose with many parts and layouts of their old amps.
 
I tried googling your amp and apparently there are several models. Not sure exactly which one yours is. I'm sure if you did a search you would be able to gather the info you're looking for.
 
As mentioned, the 6EU7's are RCA, that tube was RCA's last grasp at the consumer market...a proprietary tube that they had some patent control on. But it came as tubes were rendered obsolete in the early '60's (there was a time when tubes were a major household item, like batteries). RCA is one of a few American companies to used that etches octagon (I believe Tung Sol also used it).

I don't recognize the power tube. The combination of the side getter/flashing and the large empty area in the envelope above the plates isn't something I'm familiar with. I don't think it's American, might have been import replacement for a while back.
 
Wyatt said:
As mentioned, the 6EU7's are RCA, that tube was RCA's last grasp at the consumer market...a proprietary tube that they had some patent control on. But it came as tubes were rendered obsolete in the early '60's (there was a time when tubes were a major household item, like batteries). RCA is one of a few American companies to used that etches octagon (I believe Tung Sol also used it).

I don't recognize the power tube. The combination of the side getter/flashing and the large empty area in the envelope above the plates isn't something I'm familiar with. I don't think it's American, might have been import replacement for a while back.
Click to expand...
The octagon designation is a dead giveaway for an American tube. And I believe you're right...only RCA and Tung-sol used that marking. I don't think Tung-sol used it on all of their tubes however. I have several NOS Tung-sol tubes and if memory serves, some have that marking and some don't. I'd have to go look at them the be sure though. So don't quote me on that!!
 
Wyatt said:
As mentioned, the 6EU7's are RCA, that tube was RCA's last grasp at the consumer market...a proprietary tube that they had some patent control on. But it came as tubes were rendered obsolete in the early '60's (there was a time when tubes were a major household item, like batteries). RCA is one of a few American companies to used that etches octagon (I believe Tung Sol also used it).

I don't recognize the power tube. The combination of the side getter/flashing and the large empty area in the envelope above the plates isn't something I'm familiar with. I don't think it's American, might have been import replacement for a while back.
Click to expand...
TGP is saying that it's an RCA 6L6GC.
 
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