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dave slagle 6th November 2008 01:49 AM

A2 curves and curvecaptor.
Does anybody here know if it is possible to capture A2 curves in curvecaptor? I keep getting really odd results whenever i attempt this.

Ideally i am looking for a LTspice model of an 833A but it would be great to be able ot capture the positive part of the curves


Robert McLean 7th November 2008 01:57 AM

I found that I had to take the grid values in a certain order, for example the +4v grid values , then + 2, then 0, then -2 etc. Otherwise the program got confused. And even then when the program plotted the results they looked jumbled up. But, the actual model computed was correct, it was just the graph in curvecaptor that was odd. So I just ignored the graph, and took the models that curvecaptor computed. Of course I checked the models by running curves in spice.

You may want to take the model you get and run some curves in spice to see if this is what is happening in your situation.

dave slagle 7th November 2008 06:47 PM

hey robert.


I did as you suggested and while the results were not perfect they were at least heading in the right direction. I'll play a bit with the various fit equations to see if that changes anything.

833 curves

833 Model in Spice

the two overlapped

dowdylama 7th November 2008 07:41 PM

I really like that 4 Ampere line

kenpeter 7th November 2008 08:09 PM

What does it show for G1 current in A2?
The spice model I mean...

Spec sheet seems to stop cold for all
situations where G1>=Plate. Your curve
captor'd model seems unconcerned.

dave slagle 8th November 2008 03:29 PM

Played around and aside form the one instance where I was drawing 1E26 TA (terra amps i presume) things are looking better. (whats a hundred ma or so between friends)

I only plotted the positive numbers and had to start at 0 and go up to 350 (reordered the original file) and I got the results below. I tried numerous times to add the - bias numbers and it always conked out or gave me wacky results.


Bandersnatch 8th November 2008 05:47 PM

I keep trying to resolve why the triode clan keeps wondering about these grid curent triodes. Their plate curves are sooooo similar to pentodes...:)

SpreadSpectrum 9th November 2008 01:59 AM


Their plate curves are sooooo similar to pentodes...
At first glance they do, but there are some key differences. One being significant positive slope to the curves and the other being somewhat constant spacing between the curves. The current divisions on this plot are pretty large.

It would be interesting to overlay positive grid triode characteristics and pentode characteristics for a tube like an 813. I think pentode characteristics would give you some pretty horizontal looking lines when plotted on similar axes to the above.

Bandersnatch 9th November 2008 02:07 AM

But look at the TV sweeps that have plate Z comparable to 211's in A1...:)

dave slagle 10th November 2008 03:17 PM


Originally posted by Bandersnatch
I keep trying to resolve why the triode clan keeps wondering about these grid curent triodes. Their plate curves are sooooo similar to pentodes...:)

I have been saying this for years. I can see it now... "get pentode like perfomance and power from a 3 element structure." I will note that the A2 tubes typically do not require feedback to "clean them up"


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