I have an old Triplett Volt-Ohm-Meter. It uses tubes. Tubes for measurement devices require a very high quality tube, so that there is no fluctuation in the plate voltage.
It has GE 12AU7 tubes in it.
Tubes for measurement devices require that they be aged, or burned in for a period of 100 hours. Then the voltage is checked, and if within tolerence, can be used. Aging tubes is indeed a lost art, other than the device you plan to put them into, there's no way for the lay-person to properly age them these days.
The "12" designates the voltage, the "A" is an Audio designation, generally, a much closer tolerence tube.
I don't know what the last 2 letters stand for.
I would expect they are pretty high quality.
My father worked for GE as an electronics designer back in the 60's-70's and early 80's.
Of course, he is somewhat biased towards GE products in general, but feels GE tubes are among the best.
I believe the brand names of Telefunken and Mullard are among the most sought after NOS tubes these days. But, let the buyer beware; many of these are counterfeit.
Also noteworty is Soviet tube technology. (Or should I say former soviet) At any rate, many soviet tubes are equally sought after.
I can remember, back in the old days, when I was growing up,
7-11's and other convenience stores had "Tube Tester's" in the stores. You could could come in, plug in your tubes and test them, if one was bad, they had an ample supply in a cabinet below the tube tester. Sort of a DIY TV/Stereo repair!
I've seen NOS tubes for sale on the 'net before. Seems like they run around $25-$30 a piece.
