Bottlehead Forum

Bottlehead Finished Products => Legacy Products => Seductor => Topic started by: xcortes on January 19, 2015, 11:18:52 AM

Title: Seductor with 2.5k transformers
Post by: xcortes 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

Title: Re: Seductor with 2.5k transformers
Post by: Paul Joppa 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.

Title: Re: Seductor with 2.5k transformers
Post by: xcortes 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

Title: Re: Seductor with 2.5k transformers
Post by: xcortes 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?

Title: Re: Seductor with 2.5k transformers
Post by: Paul Joppa 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!

Title: Re: Seductor with 2.5k transformers
Post by: xcortes 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!

Title: Re: Seductor with 2.5k transformers
Post by: Paul Birkeland on January 20, 2015, 07:23:33 AM

Quote from: xcortes 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 :)

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

Title: Re: Seductor with 2.5k transformers
Post by: xcortes on January 20, 2015, 07:37:52 AM

This product was designed for me and my quads!

Thanks Pauls