I have some Valves which I cannot identify from markings on the envelops. Most are 7 or 9 pin glass Minis.

I have in the past relied to some extent on the internal structure of electrodes etc, but have recently found a couple of valves which look absolutely identical under good light and magnifying glasses .... but were clearly marked as different valves. Data sheet specs were very close .... but one was a Remote Cut-off, the other a Semi Remote Cutoff.

I appreciate that I cannot see all the 'nuances' of the Grids, Screens etc ..... but it means that some of my 'educated' guesses for a few partially marked valves based on identical electrode structures are in doubt.

What do you do with valves for which you cannot identify their markings? Throw them out? Take an educated guess and test them?? Is there an established process that people use??

Some times as noted you can tell from the internal structure & if it has a cage around the outside of the structure its likely RF. This is where the more expensive testers that one dreams about come in; like AVO.

You can actually plot how it behaves & compare it to a known that you suspect is it.

Tedious none the less

Example - 6AU6 vs 6BA6.

If not sure, I'd mark it as both. If it subsequently works in the next socket you try it in, you're ahead.

If you put it into the IF of a radio and it's unstable, you can probably mark it as a 6AU6. If on the other hand it works OK, who cares?

You could use either in the sound IF of a TV.

Sometimes it is known from experience what kind it is, for example EF89, 6BY7, 6BX6, 6EH7 and 6EJ7 all have the same connections, but physically they are different.

6AU6 and 6BA6 look identical in every way but 6BA6 is remote cutoff, while 6AU6 is sharp cutoff. I'd probably cheat and try it in a radio that uses a 6BA6 and compare the performance, although the proper way would be to use a tester and plot grid voltage vs anode current.

Another source of confusion is 6AV6, 6AT6, 6AQ6 and many other similar names and they all look identical, the only difference is the amplification factor.

Twin triodes such as 12AU7, 12AX7, 12AT7 and many more can sometimes be identified by looking at the shape and size of the anodes, compared to known ones.

6AD8 and the original version of the 6N8 look identical too, the only difference being the amplification.

My example was a 6BZ6 compared with several 6CB6A's ....

Mark, what are the AVO features which would help in the identification process?? I'm using a simple Metrix 310B tester which applies AC to all valve pins.

I will test my 'pile' of known valves first ... and this may give me a bit more experience in identifying valve types etc ..... then I will do some plotting of Plate current vs Grid voltage ...... some exciting 'mis-guided guesses' will offset the tedium .....

I was hoping there maybe an App for my iPad that I could simply wave valves in-front of and get the Identification numbers ...

It is amazing when you really check it out, just how many valves are the same, similar or just wired differently. 6B7, 6B8 are just one of several that the only difference is the socket.

There seems little electrical difference between 6M5 and 6CK6 and several other Pentodes. I looks suspiciously like the only difference with 6M5 & 6CK6 is the fact that 6CK6 uses pin 6 for the suppressor & with 6M5 its an internal connection.

Franks Electron Tube Pages has huge volumes of valve data.

If the numbers have been rubbed off, putting them in the freezer for half an hour or breathing on them will expose the ID.
But not always, JJ.