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Old 16th September 2008, 03:09 AM   #1
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Default LS50/GU50 Both Grid Drive

Oddly enough there seems to be an actual G1=G2 graph for the LS50.
I wonder how applicable it might be for the Ruskie equivalent GU50?
Looks to me about a 7K5 loadline with a reasonable 300V B+

Anyways, Zob has one (stuck in a military socket and not coming out).
And asked if I could come up with any ideas for it. He also has a 5687
burning a hole for want of a good use.

The objective is to power a Karlson K15 type, with a vintage coaxial.
Its only gonna be a monoblock.

If there are better ways to run this tube, I am not stuck on G1=G2.
But I will present the idea for comments anyway.
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Old 16th September 2008, 03:10 AM   #2
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And here is the loadline
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Old 16th September 2008, 03:35 AM   #3
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G1 = G2 makes it act like an 811, or similar tubes.. almost no plate current at VG1=VG2=0, and pulls grid current above of course...

pain in the *** to drive vs. normal triode or pentode mode... If I wanted a tube that was a pain to drive, I'd go with an 811, because it looks nice at least
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Old 16th September 2008, 05:02 AM   #4
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Pain to drive? What pain? 12 volts of swing, and all positive?
Any fifty cent op-amp could drive that...

Now that you mention it, continuous A2 draw on the grids
probably makes grid stoppers (for the GU50) unnecessary.
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Old 16th September 2008, 05:13 AM   #5
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I believe it was expropriated from Telefunken including all technological equipment and documentation at the end of the war.
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Old 16th September 2008, 05:21 AM   #6
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Seems likely to me that g1=g2 drive will quickly start drawing heavy current on g1 before the plate current gets very high. (Thus explaining George's smoked Mosfet driver experiment) Since g2 won't have enough voltage on it to draw the little e buggers thru g1 and it also shields out the plate field too. I would suggest driving g2 directly with a resistive divider down to g1, so that each grid has drive voltage scaled to 1/gm. Net result would then be a doubling of the g2 gm effectively.

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Old 16th September 2008, 05:35 AM   #7
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I have seen threads about this paralleling of grids before and just shook my head and kept silent. This is not the way a tube was designed to be used. To make a triode out of a tetrode or pentode, the screen gets tied to the plate. That is the proper way. And in so doing, the gain characteristics of the tube are changed such that the screen can operate at a higher voltage because it is in league with the plate and has less controlling effect. Screen and control grid do not get connected together. This is the way I was always taught.

Yet every so often people will go against the grain and try making a triode by tying them together. Has no one told them that is incorrect? That the usefull characteristics of a tube are destroyed? Perhaps I am too set in my ways and too old to learn new tricks. But I think not. IMHO using a tube in this maner is about as cockamamie as inverted tube operation. Maybe it's the fun of doing something one shouldn't or the joy of an exercise in near futility. I just don't know.

Ok, end of rant.
Victor
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Old 16th September 2008, 07:08 AM   #8
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I am going to try a double-drive such a way:
1. Differential phase splitter,
2. 2 asymmetrical Concertinas (higher value of resistors in anodes) coupled to each anode of a diff stage directly;
3. Source followers from their anodes to screen grids of output pentodes,
4. Capacitive coupled cathodes of Concertinas to control grids of output pentodes.
The result should be kind of opposite to UL mode.
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Old 16th September 2008, 08:54 AM   #9
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Quote:
Perhaps I am too set in my ways and too old to learn new tricks. But I think not. IMHO using a tube in this manner is about as cockamamie as inverted tube operation. Maybe it's the fun of doing something one shouldn't or the joy of an exercise in near futility. I just don't know.
"You are old, Father William," the young man said,
and your grids are uncommonly driven.
Yet you ran your load lines to positive twelve,
despite the data that's given?"

"In my youth," said the sage, as he soldered the joint,
"I chose to run conventionally;
but with these new options I find that I can
increase power sensitivity."
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Old 16th September 2008, 10:10 AM   #10
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Quote:
Originally posted by SY


"You are old, Father William," the young man said,
and your grids are uncommonly driven.
Yet you ran your load lines to positive twelve,
despite the data that's given?"

"In my youth," said the sage, as he soldered the joint,
"I chose to run conventionally;
but with these new options I find that I can
increase power sensitivity."
Brilliant! Now on solid state, topic "running in class B".

Jan Didden
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