Here's another one ... - Lynn Olson - K&K Audio / Lundahl Transformers

Here's another one ...

Posted by Lynn Olson (M) on December 11, 2003 at 17:34:23

In Reply to: An aside your thoughts suggested... posted by JamesD on December 7, 2003 at 05:16:45:

Here's another variation to minimize input capacitance. It takes advantage of four identical triodes - in theory at least, each "side" should consist of one composite device, a cathode-follower with a grounded-grid amplifier. There should be some cancellation of device nonlinearity since they are effectively in a totem-pole configuration, like a folded cascode.

Input capacitance is the same as a cathode follower, only a few pF, about half of which is socket capacitance. Output impedance of the amplifier is probably double that of a standard circuit.

The blue lines show an alternate connection with twice the gain, since all grids are driven. This removes the capacitance cancellation, but does give twice the gain of a standard amplifier. I have no idea what the output impedance is ... I leave that as an excercise for the reader. Maybe the same as the other circuit.

Note current balancing feature ... if the resistance of the pot is the same as the DC resistance of the primary on the output transformer, each plate sits at the same voltage, and the pot trims the current going through each "side."

Kinda pleased with this one - have fun, Gary P and JamesD!

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Follow Ups Full Thread

Topic - Hello JamesD, really enjoyed your posts - Lynn Olson 21:39:33 12/02/03 (22)

Re: Hello JamesD, really enjoyed your posts - JamesD 06:34:05 12/05/03 (15)

Re: Hello JamesD, really enjoyed your posts - Gary P 08:54:12 12/06/03 (2)

Just a quick thought... - JamesD 00:01:11 12/07/03 (1)

Found the Diyaudio thread but incomplete data... - JamesD 03:51:11 12/07/03 (0)

Assorted Thoughts - Lynn Olson 14:21:20 12/05/03 (11)

Like Bas, I love the recollections! - James D. 04:14:30 12/07/03 (0)

Better Math - Lynn Olson 21:01:31 12/05/03 (0)

Mo' Thoughts - Lynn Olson 15:50:06 12/05/03 (8)

An aside your thoughts suggested... - JamesD 05:16:45 12/07/03 (7)

Here's another one ... - Lynn Olson 17:34:23 12/11/03 (2)

Re: Here's another one ... - JamesD 12:39:27 12/14/03 (1)

Unusual behavior from grounded-grids ... - Lynn Olson 14:59:23 12/14/03 (0)

It boils down to a pentode CF driving a GG triode - Lynn Olson 13:56:45 12/07/03 (3)

Re: It boils down to a pentode CF driving a GG triode - JamesD 08:27:07 12/09/03 (2)

Setting up the bias - Gary P 12:00:45 12/10/03 (1)

Re: Setting up the bias - JamesD 03:50:58 12/11/03 (0)

Hi Lynn..yes finally someone else I like to read.... - Bas Horneman 08:02:53 12/04/03 (3)

Argh... Bas, how could you do this to me? - JamesD 06:36:51 12/05/03 (2)

Not really pressure James...you would be suprised how - Bas Horneman 13:53:58 12/06/03 (1)

I agree! - JamesD 04:17:07 12/07/03 (0)

12B4A? - keto 22:30:07 12/03/03 (0)

Hmm , interesting schematic - IslandPink 07:33:54 12/03/03 (0)

Follow Ups

Here's another one ... - Lynn Olson 17:34:23 12/11/03 (2)

Re: Here's another one ... - JamesD 12:39:27 12/14/03 (1)

Unusual behavior from grounded-grids ... - Lynn Olson 14:59:23 12/14/03 (0)

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