anyone know what these valves are?

[norburybrook]

been given a bag of valves and I have about 10 of these but there's no marking so was wondering if anyone can tell what they are?



Marcus

[dorrisant]

Do you have a tube tester? If so pop them in and test as if they were 12AX7s... Gotta be in that family.

[norburybrook]

I don't I'm afraid , just popped one in an amp and it's very low gain.

Can I damage my amps if I'm not sure what they are? they look like 12AX7's to me. They look like old Mullards with the Halo getter and the ridged plates. might be AY7's or some other lower powered version.
'
M

[Phil_S]

If they all look about like the one in the middle (the particular rotation in the picture), I think it's a pretty safe bet you've got dual triodes. You might try tracing some of the internal structures to the pin connections. Maybe you'll get lucky. I'd say if you can identify any one structure (plate, grid, cathode, heater) to a particular pin#, you are half way there. Once you have 2 of them, you're almost home. For example, if you can see that pin 1 is a plate/anode and pin 6 is a cathode, it's a pretty good bet you've got a 12A?7 family tube. If you can see heaters are pins 1 and 2, I'd go for 6EU7's. Some luck will be needed.

Next, try putting them in the freezer. Let them get good 'n' cold. When you remove them, very briefly, you may be able to see or raise an image of the tube ID by blowing some hot breathe on it.

Whether you'll get anything definitive, who knows? It's worth trying.

[dorrisant]

Good tip on the freezer trip Phil... I like your "cryogenic" deduction.

[tictac]

The tube on the far left looks like a Telefunken smooth plate.....

TT

[Stevem]

They all look like some kind of duel triode, and that center one looks like a 12AT7.
Without knowing what they are popping them in a tube tester may not do you much good unless it's a type of tester that checks for GM / transmutual conductance, then you could see have fast the tube responded to the test function somewhat and get a ball park for what it might be due to gain.
On a non GM type tester dropping down the Heater voltage is the right only way to see if your testing the tube with the right setting!
If the tube is good that you are are testing at 12.6 volts and you drop down to about 10 volts then it's emission will not take a big nose dive.