Independently Re-discovered - Lynn Olson - K&K Audio / Lundahl Transformers

Independently Re-discovered

Posted by Lynn Olson (M) on June 8, 2004 at 11:25:36

In Reply to: Re: No Effect for a PP Circuit posted by Dave Davenport on June 8, 2004 at 05:38:35:

By John Atwood of One Electron (see URL below). He's the one with the Audio Precision test set, a test amplifier, and links to the original WE articles.

The actual test amplifier has independently biased triode-connected 6CK4's (each with its own adjustable current source), and a pair of 1000uF electrolytics in series between the two cathodes. The center-point of the two caps can be returned to ground, left open-circuit, or connected to a 500-ohm pot. If it is returned to ground, that is equivalent to normal cap-bypassed Class A PP amplifier; if it left open, that's equivalent to the Allen Wright current-source approach; and if the variable resistor is chosen, that's similar to the WE Harmonic Equalizer.

Note the test amp is not designed to be listened to, but make a series of measurements. I expect John will re-test with battery-heated 2A3's at some point in the future, although these results are similar to what other people have seen with 300B's.

Although there is no change in output Z with common cathode source impedance, the distortion nulling, although broad, has some sensitivity to the load the output tubes see. For a 2K pri impedance (very low), 20 ohms is about right; for 10K or higher, 100 ohms is about right. But the 3rd and 5th-harmonic nulls are quite broad, so a 2:1 or 3:1 mismatch error in resistor value is not significant.

So it doesn't really make any difference if the 20 to 100 ohms series resistance is added to a conventional cathode-bypass capacitor, a WE-style shunt cap, or the cathode resistor is split in two (450 + 50 ohms, for example) and the cap connected to the center point of the two resistors.

Close examination of the WE86 (visit the Nutshellhifi.com Library for PDF) schematic also discloses an unusual network attached to the grid circuit - we're still discussing what that does.

John Atwood - One Electron (Open in New Window)

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Follow Ups Full Thread

Topic - Question about Olson's Karna and LL1635 - arend-jan 09:57:55 05/30/04 (22)

Re: Question about Olson's Karna and LL1635 - KevinC 12:42:55 05/30/04 (20)

Re: Question about Olson's Karna and LL1635 - Charlie G 22:54:37 06/03/04 (1)

Re: Question about Olson's Karna and LL1635 - KevinC 05:50:16 06/04/04 (0)

Re: Question about Olson's Karna and LL1635 - arend-jan 04:24:28 06/02/04 (17)

Re: Question about Olson's Karna and LL1635 - KevinC 14:49:16 06/02/04 (16)

My observations - IslandPink 08:32:26 06/04/04 (15)

Re: Thoughts, possibly off target ... - Mike C 06:39:31 06/10/04 (3)

OK, and Harmonic Compensator - IslandPink 01:29:09 06/11/04 (2)

Re: OK, and Harmonic Compensator - arend-jan 07:17:50 06/11/04 (0)

Re: OK, and Harmonic Compensator - Dave Davenport 04:41:13 06/11/04 (0)

Try This - Lynn Olson 00:18:18 06/07/04 (6)

Re: Try This - Paul Barker 10:25:42 06/07/04 (4)

No Effect for a PP Circuit - Lynn Olson 00:06:00 06/08/04 (3)

Re: No Effect for a PP Circuit - Dave Davenport 05:38:35 06/08/04 (1)

Independently Re-discovered - Lynn Olson 11:25:36 06/08/04 (1)

Thanks - Paul Barker 00:43:21 06/08/04 (0)

Aha, the second order question - IslandPink 05:48:17 06/07/04 (0)

Re: My observations - Stephen R 23:02:24 06/04/04 (1)

Plot thickens - IslandPink 11:50:25 06/06/04 (0)

Re: My observations - KevinC 11:19:53 06/04/04 (1)

Yes, both - IslandPink 15:41:22 06/04/04 (0)

Follow Ups

Independently Re-discovered - Lynn Olson 11:25:36 06/08/04 (1)

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