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Old 30th July 2008, 11:19 PM   #1
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Default DIY U-L curves

hey-Hey!!!,
I use U-L curves, and I have a reasonable system for drawing them, if the data sheet has enough information. Then I can check the load line and where the outer boundaries of the tube characteristics lie( what goes on in the middle is not so important; fixed bias deals with the required g1 voltage).

I have a sketch scanned to pdf, but it is nearly half a Meg. Any help getting it loaded would be much appreciated. It is farily simple, but I wanted to improve it...
cheers,
Douglas
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Old 31st July 2008, 12:41 PM   #2
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here are some curves...

They're shrunk to the point of loosing a lot of resolution. In the upper one, the AB halving of the load( from 3k3 to 1k65 )turns up at around 220V. That one started from 400V. Both sets drive the load line out through the 'top' to the righ of the knee.

In the lower one, the UL starting point was 350V, and it works out Class A with a 6k4 a-a( 3k2, but note the upper curve; the 1k6 is barely steeper ) so 6k6 a-a would be just fine.

Douglas
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Old 31st July 2008, 01:15 PM   #3
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better?
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Old 31st July 2008, 07:09 PM   #4
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I think that curve set may be for screen driven g2 (g1=0).

You have overlay'd the g1=0 triode curve onto it, I'm not
quite sure how the fusion of these graphs is being abused
to discombobulate UL??? Care to elaborate?
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Old 31st July 2008, 08:50 PM   #5
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Quote:
Originally posted by kenpeter
I think that curve set may be for screen driven g2 (g1=0).

You have overlay'd the g1=0 triode curve onto it, I'm not
quite sure how the fusion of these graphs is being abused
to discombobulate UL??? Care to elaborate?
I do seriously doubt that the g1=0/variable g2 curves were published for screen drive operation.

I also did not get curves, I got the upper, g1=0 curve; the outer envelope. That is what is most useful. The process is simple. For U-L, at idle g2=anode voltage, so pick a starting voltage on a g2 line. depending on what the U-L percentage is, find anode voltage delta for a g2 delta equal to the spacing. At that plate voltage on the new g2 curve is an operating point. The line drawn between starting point and the new one is roughly the shape of the g1=0V curve of U-L starting point and percentage.

I drew the triode lline so that one could download the whole GE data sheet and compare to the triode curves. They do overlay, or did yo not bother looking yet?
cheers,
Douglas
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Old 31st July 2008, 11:58 PM   #6
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Quote:
Originally posted by kenpeter
40%UL
G1=0V
So far so good I think. As with all U-L curves, stating the starting point is important. In your case it looks like 400V.

Note plate Z of ~2k, v. the triode at ~1k. At moderate negative bias the plate Z is likely more like 3k. Still a worthy improvement over the pentode...
cheers,
Dougals
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Old 1st August 2008, 12:04 AM   #7
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G1=0V , G2=400VDC-40%UL
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Old 1st August 2008, 12:14 AM   #8
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Sorry I deleted that, I thought (in error) I had made some error.
But then realized I had drawn correctly, and promptly reposted.

Anyways, I see now you weren't drawing some kooky folded
AB load line. Merely a slightly truncated version on the same
exact red 40% line I just drew. Only the lower "fold" of your
composite graph was intended to illustrate the loadline...

It just looked strange, and threw me for a moment.
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Old 1st August 2008, 12:46 AM   #9
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Quote:
Originally posted by kenpeter
Sorry I deleted that, I thought (in error) I had made some error.
But then realized I had drawn correctly, and promptly reposted.

Anyways, I see now you weren't drawing some kooky folded
AB load line. Merely a slightly truncated version on the same
exact red 40% line I just drew. Only the lower "fold" of your
composite graph was intended to illustrate the loadline...

It just looked strange, and threw me for a moment.
That whole load-line thing was from an ongoing discussion I've had with some folks over why 6k6 seems to fit the 6L6 so well. For U-L it certainly does, but there are lots of variables... We could also draw a 20% U-L curves. For the U-L tapping discussion it is useful, but perhaps with advanced warning, yes?
cheers,
Douglas
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Old 1st August 2008, 01:18 AM   #10
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I think these G1 lines must aproximate -0.5V spacing?
Start drawing from 400/400, 350/350, 250/250 triode.

Hard to tell, cause 250V/250V pentode doesn't match
250/250 G2... GE's graphs don't even seem to agree
with themselves... G1 would still be about 0V, makes
no sense at all...

And published Triode curves don't go that high in mA...

So I am fudging from way down at 150/150 triode =
-2.5V@G1. And should intersect my 6th UL curve if
I had continued drawing more of them.... Must eq
-0.5V per grid line, to be near -2.5V by the 6th line....
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