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Old 29th January 2010, 09:23 PM   #1
db! is offline db!  Canada
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Default Finding triode curves

I have several power tetrodes(transmitter tubes) that I want to build an amp out of. Unfortunately, the datasheets only give the Grid voltage Vs Plate voltage instead of the plate current vs plate voltage graph. Is there a way to mathematically derive the required graph?

Any help would be appreciated!
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Old 30th January 2010, 06:28 AM   #2
Svein_B is offline Svein_B  Norway
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If you want to do it mathematically, you could get some indicative curves by using LtSpice.

Spice curvetracing how-to:
:: View topic - Tube plate curves
Tube Simulation with PSPICE: Tips, Tricks, Techniques

This of course requires that you have pentode spice models for the tubes.
If not, there are even ways to generate these form just a screenshot of plate curves:
Model Paint Tools: Trace Tube Parameters over Plate Curves, Interactively


Below is an example of curve traces from Ltspice with El84/6BQ5 wired as pentode and triode compared to the published curves.

Svein.
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File Type: gif EL84-spice-traces.gif (111.3 KB, 347 views)
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Old 30th January 2010, 08:04 AM   #3
db! is offline db!  Canada
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Thanks for the Suggestion; As promising as the software looks, my computer won't run it for some reason... I've clicked on the executable several times and nothing happens .
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Old 31st January 2010, 01:08 PM   #4
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Default Run paint tool

Hey,

make shure you install a JAVA runtime version >= 1.4 on your computer. Aslo check the PATH variable like:
windows:
echo %PATh%
Should include a PATH like C:\programs\JAVA\1.5.15\jre\bin
UNIX:
echo $PATH
Should include a PATH like /opt/java/1.5.15/jre/bin

simply check this by typing in at the shell "java -version". There should be the installed version printed out.

To start model patin type in:
java -jar paint_kip.jar ( for pentodes) or java.jar paint_kit.jar ( for triodes )

Well, it´s not my farvorite tool. I never bring the curves to concident usind all the slides. For triodes try to use "curve captor". It´s easy, fast and produce a very matching space output.

Have fun..

Karsten
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Old 31st January 2010, 02:39 PM   #5
Serge66 is offline Serge66  Switzerland
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Hi,
Anything here:
Frank's electron Tube Data sheets
Cheers,

Serge
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Old 31st January 2010, 09:10 PM   #6
db! is offline db!  Canada
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Karsten21 - Thanks for the tips. Unfortunately, I still can't get the program to work.

Serge66 - I can only find the datasheet; there are no triode curves.

Unfortunately, the datasheets for the tubes I want to use do not have a Plate V - Plate current plot. They only provide a grid V- plate V plot; I'm not too sure how to go about this since all the methods of deriving the triode curve rely on the plate V-plate current...

Any thoughts?
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Old 31st January 2010, 10:27 PM   #7
Glowbug is offline Glowbug  United States
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What are the tubes you're using?

Ham radio resources would be another avenue I'd check out...hams have a lot of info about transmitting tubes of all kinds, and the old ARRL Handbooks were great sources of tube operation info.
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Last edited by Glowbug; 31st January 2010 at 10:29 PM.
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Old 31st January 2010, 11:24 PM   #8
db! is offline db!  Canada
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I am looking into using the 4x150 and various other 4-xxxA series tubes that I have lying around. Unfortunately, these tubes were never designed for use in triode mode so the triode curves were never documented.
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Old 1st February 2010, 01:47 AM   #9
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Quote:
I am looking into using the 4x150 and various other 4-xxxA series tubes that I have lying around.
Unfortunately these tubes don't work too well as triodes. The maximum screen grid voltage for the 4X150 is 300 volts. The maximum for the 4CX250 is 400 volts. I blew up a 4CX250 to find out that this rating is real. I have several more. They will probably wind up in a 2 meter linear amp.
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Old 1st February 2010, 03:10 AM   #10
db! is offline db!  Canada
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Thanks for pointing that out; I completely forgot to look at the screen voltages! I will need to look over the datasheets for several other tubes before deciding.

Now for the stupid questions/ideas/suggestions:

Would it work:

- Grounded grid mode
- Strapping the two screens together
- Leaving the unwanted screen disconnected
- Grounding the unwanted screen

Any info is appreciated!
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