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In the Forum: Analog Playback
In the Thread: 7788 tube mic pre design
Post Subject: Some useful curvesPosted by hagtech on: 11/5/2007
Ok, so it took me awhile.  I finally got around to doing a design around this tube, believe it or not, as a driver for a 2A3.  It just seemed right.  Bought some 60's vintage(?) Amperex "PQ" on eBay.  Well, here's what it looks like:



That's 50V/div horizontal, 12.5mA/div vertical.  Screen at about 200V.  The looping caused by a power supply time constant in my curve tracer (the loop ain't real).  I forget where zero is.  I think this was 0.5V per grid step.  The severe kink makes this look like a tetrode.  In fact, maybe that's because I hooked it up as a tetrode?  Aw crap, I left pin 8 floating.  Anyway, here's the triode-strapped version:



Looks incredibly linear.  The kink is still there.  I let you know tomorrow if it is real.  Grid steps are 1V/div, starting at 0V.  Turns out plate impedance is about 2.8k, mu is roughly 50.  Linearity is awesome.  Shoot, I guess that makes this a supertube.

jh

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