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12T10 triode connection - similar "real" triode to compare to?

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I'm still messing around trying to make the best use of the "dual-control pentode" section of this tube. It doesn't make a very good ordinary pentode. Pete Millett (The Mighty Midget) has found one clever trick, which is to bias up G3. But this is a little more complex than I'd like and hard to make work for a LTP. I'm testing it connected at a triode right now.
Attached is set of curves I measured for this setup. I'm wondering if the characteristics are close enough to some "real" triode that I could crib some ideas from other designs.
Is there a database or something somewhere that would let me look up tubes by their electrical characteristics? Or maybe some of you can just eyeball it and associate it with a known design.
Thanks.
 

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I just did a little experimenting on a 6LE8 here, which is a dual control type tube.
(I connected the two plates together, and the two g3's together for this to act as one tube) And connecting g3 to plate, with g2 to g1, does not get much current out. So skip that previously mentioned idea.

Positive +12V on g3 (and +100V on g2) makes for a super nice pentode, but that is well known.

I did find a new configuration of interest however. Connect g3 to plate, and then about +50V on g2, this makes for something like ultralinear curves with tetrode kinks in the 0 to 50V plate voltage range. As long as the plate V stays above +50V though, its a nice "UL triode like" configuration (pentode like knees, but triode like curves, similar to class 2 triode operation, but no g1 grid current here).
The "UL triode" config does have higher Rp than the g2 and g3 connected to plate version.
 
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It seems pretty close to the 12AV7... anyway, would you have the triode curves for the other pentode section as well?

No, I haven't tried that. It puts out just barely enough "oomph" right now, I think I'd lose too much if I connected them as triodes.

Also not sure how well the tubes would hold up. I toasted another one (#3 so far), this one was section #2 (dual control) and it was by running it just slightly past the rated screen dissipation for maybe 15 minutes. It behaved as though it has lost about a 1/3 of it's conductance (emissivity?). I'm guessing that by the end of the tube era (these Compactrons date from the late 60's and early 70's) they were cutting costs and designing right to the hairy edge of the published specs.

But they are awfully cheap... :D
 
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[/B]No, I haven't tried that. It puts out just barely enough "oomph" right now, I think I'd lose too much if I connected them as triodes. Also not sure how well the tubes would hold up. I toasted another one (#3 so far), this one was section #2 (dual control) and it was by running it just slightly past the rated screen dissipation for maybe 15 minutes.
Sorry if I was not clear... I need the triode curves for section 1 for another project, not suggesting that you use it in yours. If you run section 2 as a voltage amplifier, it should not burn up at all. Only section 1 should be used as the output stage... may be you can show a schematic of what you are trying to do?
 
jazzbo8
Sorry if I was not clear... I need the triode curves for section 1 for another project, not suggesting that you use it in yours. If you run section 2 as a voltage amplifier, it should not burn up at all. Only section 1 should be used as the output stage... may be you can show a schematic of what you are trying to do?

Right now I've got the pentode halves set up as P-P and am working out how to use the triode connected section 2's as a LTP to drive them. I'll put up a schematic of the results when I get there, and when I tear it down I'll make some curves for the section 1 (beam pentode) side as a triode. But the way things are going right now it could be awhile.
 
I may get the triode curves for the beam sections for myself in any case.

For what it's worth the triode connected dual-control sections made a nicely behaved LTP, but the best gain I could get was about 10, which isn't quite enough for my application. The problem is that a LTP cuts the tube's "natural" gain approximately in half, so you need a fair amount to start with. I'm working with the pentode connection now, elevating G3 positive (this is in another thread)
 
When the g3 is pulled up positive for the best square knee'd plate curves on these dual control tubes, there is less (about 1/2) g2 screen current, saving around 1/2 a Watt for the screen for this tube (12T10). (bottom page 8 and top page 9 on the datasheet)

The usual rule for TV sweep tubes is that for every screen Watt reduction, the plate can be increased by 4 Watts. Whether you could get 2 more Watts of plate dissipation, you'll have to look at the plate size to judge. But very likely another Watt is available at least. Might help with reducing the plate load resistor some for driving the next grid.

The 6BV11 dual control tubes have nice big plates, I haven't seen a 12T10.

http://frank.pocnet.net/sheets/123/6/6T10.pdf
 
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Hi,

Afaik the 12T10 is a very close equivalent of 12AD10.
I did some experimenting with the latter a few years ago and was very surprised at what beating it would take.
At first the dualcontrol section was triode-strapped and used for a split-load P/I.
That wasn't such a hot idea; I got all kinds of instability that I couldn't control.
Especially ultrasonic oscillation, possibly because of inter-electrode capacities.
Screening helped but didn't cure.
I was ready to give up the idea of using the control-pentode section for anything when I thought it would be interesting to see how the power-pentode section would run in Class AB2.
I again strapped the control-section for triode and used it as a cathode-follower driver for the output section; see the attached schematic.
That idea led to some very satisfying results using an Edcor CXPP30-MS-3.8K OPT.
At one point during experimenting, the output-pentodes were dissipating (A+G2) ~26Watt each at B+ =340V and still not red-plating ! (RCA-tubes)
Running as per attached schematic, output is around 12Watt/Triode-mode in full AB2, which is actually taking G1 to +12V.
About 4x the power of running Class AB1 with the same circuit.

I'm also attaching various curves for the 12AD10. They should fit the 12T10 nicely.

rgds,

/tricomp
 

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  • CF- AB2-Drive for 6AD10.pdf
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  • 6AD10_Curves.pdf
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