Dual Triode Tube Testing, Curve Tracer

[W5FH]

Hello-
    I had mentioned in a previous post a dual triode that is of interest, the Tungsol TS-272. This tube is similar to the 12AX7 it appears to me. The physical differences are a 6.3 VAC filament between pins 4 & 5 (no center tap) and a shield (connected to pin 9) separating the two triodes. I wanted to ask some of the more tube-knowledgeable folks here about my testing results. I have a TV-7D/U that I have used to test many dual triodes like 12AU7, 12AT7 and 12AX7. When I set the tester up with 12AX7 settings (with 6.3 VAC on filament) the TS-272 tests very close to the 12AX7 in transconductance. The bulk of my 12AX7 tests range between 38-48, with some up to as high as 60 on the transconductance test. These TS-272 tubes test pretty consistently around 52-54 on transconductance test using same 12AX7 settings. I tried the TS-272 at 12AU7 and 12AT7 settings and it was way different on transconductance as compared to those tubes. What is this telling me? If 2 tubes test similar in transconductance does that mean they will behave similarly? I was curious if anyone here has a tube curve tracer that could look at these TS-272 tubes? The reason I am interested is because I stuck back a couple of 1 gross bulk packs out of surplus finds. Many of the tubes have tiny numbered stickers on them, or have different colored dots painted on them. Was considering using them in preamps if they are similar to 12AX7. 

[PRR]

Transconductance is not the whole story.

But if you have two gross of these bottles, just try one.

[HotBluePlates]

... the Tungsol TS-272. ... When I set the tester up with 12AX7 settings ... the TS-272 tests very close to the 12AX7 in transconductance. ...

Transconductance is not the whole story. ...

This is where the otherwise cumbersome Russian L3-3 shines.

You can create your own curves by setting a grid voltage, then dialing the plate voltage from 25v up to 300v or more.  Plot your points, change to a new fixed grid voltage, and repeat the plate voltage sweep.

... Was considering using them in preamps if they are similar to 12AX7. 

But if you have two gross of these bottles, just try one.

Re-wire 1 socket and give them a try in an amp.  If everything is basically-unchanged, you know you're close-enough to 12AX7.