I found some NOS tubes

[Ampclutz]

Hi All,

I got a bunch of NOS tubes left over from an estate sale. They are Gamma-Tron branded but they are obviously rebranded from other manufacturers. I have a bunch of different 6SN7 tubes and there are about a dozen different "varieties". I may have to start a museum of tubes! I have GT, GTA, GTB, long medium and short tubes, shiny black plates, not so shiny black plates, grey plates, triangular plates, round plates, black glass, grey glass, clear glass, top getters, bottom getters, side getters, chrome tops, long chrome tops, even a couple of mickey mouse ear tubes. I had no idea there were so many different kinds of the same type tubes! I see a display case in my future.

I got most of a box of 25L6GT tubes. That is about 100 tubes minus a few.

Here is where I need a little help... There are several different "flavors" of 25L6's. Black glass, grey glass, clear glass, markings on the top, markings on the side. They are all octal bases but some have 6 pins and some have 7 pins. The ones with 0740 on the side of the glass have me scratching my head... Some have 0740 on the glass and 25L6GT on the base. Some just have 0740 on the glass. I can't seem to find a data sheet for a 0740 tube.

Can somebody enlighten me about the 0740 designation? Please...

Thanks,

AC

[quayhog]

7th week of 1940?

[Enzo]

The 25L6 will have pin 6 missing, and pin 1 may or may not be missing depending upon who made it. This tube is the same as the 50L6 except the heater.

I have an old Guild amp in here with a bunch of 50L6 in it, coincidently.

The tube is only good for about 200v on the plate and only a few watts. It is NOT a 6L6 with different heater.

0740 sounds like a date/lot code to me too.

[Ampclutz]

Thanks for the information. All useful.

So far I have found six different 25L6GT tubes. And I thought all of the same numbered tubes were the same... I find this strangely interesting. Now where IS that display case!

AC

[Steve Conner]

Sounds like a nice find! When I moved into my apartment, the previous owner had built a display case into an alcove in the living room. So I had to fill it with tubes

I used to have this mercury vapour rectifier rigged up so it would light up, but the heater power supply died and I haven't got round to fixing it. I don't have any mickey mouse ear tubes yet

[Enzo]

Same numbered tubes are the same the way same numbered tires are the same. Even today, look at all the various 12AX7s on the market. They don't look the same either.

25L6, or 6L6, or 12AX7, or whatever specifies performance parameters. The tube maker constructs it the way they wish, within certain limits of course.