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Old 16th December 2008, 04:38 PM   #1
bigwill is offline bigwill  United Kingdom
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Question Diff drive

Came up with a simple idea today, wondered if it has ever been tried. The basic idea is having a differential driver (not a phase splitter) that can take feedback from the plate to linearise and lower the impedance of a pentode or tetrode (or further linearise a triode)

See image for the circuit I thought of

Last edited by bigwill; 11th September 2012 at 09:41 AM.
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Old 16th December 2008, 04:48 PM   #2
bigwill is offline bigwill  United Kingdom
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Oops, assume the bottom triodes are upside down Forgot to make the cathodes look different

On another side note I'm amazed how inarticulate I feel today after being around the people I work with
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Old 16th December 2008, 06:20 PM   #3
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Bigwill,
I assume that you wanted negative feedback to accomplish your goals. Following it through from tube to tube, it seems to me that you've got positive feedback as drawn. Perhaps cross coupling the feedback points would more efficacious.

Victor
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Old 16th December 2008, 06:33 PM   #4
bigwill is offline bigwill  United Kingdom
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Quote:
Originally posted by HollowState
Bigwill,
I assume that you wanted negative feedback to accomplish your goals. Following it through from tube to tube, it seems to me that you've got positive feedback as drawn. Perhaps cross coupling the feedback points would more efficacious.

Victor

Hmm, are you sure?

Input signal goes to first grid, positive going signal lowers anode voltage on first valve, causing the output valve to switch off more thus also having a positive direction on ITS anode, which is then coupled to the other side of the differential, turning on that side more and turning off the driving side to cancel it out

Is this right?
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Old 16th December 2008, 06:44 PM   #5
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Following the phase:

plus in to 1st tube

neg out at plate

neg in at 2nd grid *

pos out at plate

pos in at output tube

neg out at plate

neg in at feedback grid

neg in at cathode *

same phase equals positive FB
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Old 16th December 2008, 07:01 PM   #6
bigwill is offline bigwill  United Kingdom
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Damn, it seems you're correct

Back to the drawing board!
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Old 16th December 2008, 07:06 PM   #7
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The design is interesting, just cross couple the feedback and you'll be cool.
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Old 16th December 2008, 07:06 PM   #8
lineup is offline lineup  Sweden
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for a differential pair
we want the same phase on both inputs
to get negative corrective feedback

this will strive to keep the diff pair both input voltages in balance

so, i think the circuit is correct .. ??
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Old 16th December 2008, 07:19 PM   #9
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Quote:
Originally posted by lineup
for a differential pair
we want the same phase on both inputs
to get negative corrective feedback

this will strive to keep the diff pair both input voltages in balance

so, i think the circuit is correct .. ??
That is how I read it.

I put a little arrow at each input and output. Up for increasing and Down for decreasing is simple enough...
cheers,
Douglas
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Old 16th December 2008, 07:35 PM   #10
bigwill is offline bigwill  United Kingdom
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I think I've changed my mind, I'm pretty sure it's negative feedback


Starting at the diff pair


signal goes UP

left hand anode goes DOWN

causing OUTPUT tube anode to go UP

driving right hand of diff pair UP

causing ITs anode to go DOWN

thus making the left hand anode opposite go UP, against its downward... ness
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