Seductor with 2.5k transformers

xcortes · 3786

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Offline xcortes

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on: January 19, 2015, 11:18:52 AM
Sorry if the question is stupid for pentodes as I've never worked with them. Would a Seductor work with 2.5k output transformers? What are the tradeoffs here?

How about 5k?

Thanks
« Last Edit: January 19, 2015, 11:31:14 AM by xcortes »

Xavier Cortes


Offline Paul Joppa

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Reply #1 on: January 19, 2015, 12:18:03 PM
It should work; the tradeoff is less power before clipping, and asymmetrical clipping. Pentodes are quite a bit more fussy about their load.

Paul Joppa


Offline xcortes

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Reply #2 on: January 19, 2015, 02:04:27 PM
Thanks Paul.

How much less power?

Also, how about paralleling the two output tubes and using a single output transformer? Is that possible?

Thanks again
« Last Edit: January 19, 2015, 02:21:49 PM by xcortes »

Xavier Cortes


Offline xcortes

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Reply #3 on: January 19, 2015, 03:17:18 PM
I think I can answer some of my own questions (and then ask others):

Paralleling the pentodes is not such a bad idea as " the argument against parallel applies to SETs. Pentodes, being more like current sources, are happier in parallel" (PJ)

The only problemis that in the design the output transformer is not grounded but returned to the bias voltage of the output tube. If this can be changed and the transformer can be grounded a single 2.5k transformer would work great for both tubes.

Tha transformer is supposed to be for 3.5W but baing a Magnequest and a Cobalt one it ought to work perfectly fine for 8 watts.

Am I right so far Paul?

Xavier Cortes


Offline Paul Joppa

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Reply #4 on: January 19, 2015, 06:25:52 PM
My experiments with parallel pentodes are still in work, so I don't have have anything solid to offer. Still discovering unanticipated problems!

Meanwhile, Seductor has most of its feedback local to each output stage, so the impedance into the stock transformers is low and they can be in series at their outputs with no problems.

Sorry, I really don't know how much less power for off-spec output transformers. I would expect a bit more than half for the impedances mentioned, but it's pentodes, my expectation is not founded on much data or good analysis. Ask again in a few years!

Paul Joppa


Offline xcortes

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Reply #5 on: January 20, 2015, 04:30:34 AM
Thanks Paul,

I guess it's time for me to (finally) build a BH kit completely stock :)

From what I understand the iron included is pretty good!

Xavier Cortes


Offline Paul Birkeland

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Reply #6 on: January 20, 2015, 07:23:33 AM
Thanks Paul,

I guess it's time for me to (finally) build a BH kit completely stock :)

I left a nice amount of room for a beefy 3.3uF cap on each side.  We also have more primary windings options available, so dialing things in with funky line voltages is less difficult than it has been in the past.

-PB
« Last Edit: January 20, 2015, 11:25:12 AM by Caucasian Blackplate »

Paul "PB" Birkeland

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Offline xcortes

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Reply #7 on: January 20, 2015, 07:37:52 AM
This product was designed for me and my quads!

Thanks Pauls

Xavier Cortes