Re: I read most of your posts, and find you to be very knowledgeable ...

Will,
I believe that your RECOMMENDATION of going to 6K primary is a good one BUT I think your explanations down further in the text might be exactly backward.

a 6K to 4 Ohm output transformer will, given the same output stage, provide a better drive of lower impedance speakers than say a 3K4 to 4 ohms.
WHY?
The output tubes will have a characteristic output impedance due to the tubes rp. The higher the turns ratio the lower the reflected impedance in the secondary which is the same as saying the lower the output impedance of the amplifier. Hence better damping factor and better drive of low impedance loads.
Thats why I think Ultralinear is a good idea too, (the tubes rp is lower), not as low as triode mode but a lot less than pentode mode.

Having said that there are, as you suggest, trade offs.

A lower primary impedance meams that you can develop full output power with less voltage swing => lower High Voltage supply required => you can run the tubes at higher idle current (for same dissipation) = > lower tube rp.

ALSO

Lower turns (impedance) ratio transformers are easier to construct and usually means that they have lower leakage inductance and shunt capacitance, both of these things will help with high frequency response.

Balancing all these things is what high end audio design is all about.

This may be a good read:
http://www.turneraudio.com.au/loadmatch4-pp-beamtetrodes.html

Actually there is a fair bit on Patrick Turners webpages which is worth a read.

Cheers,
Ian

This post is made possible by the generous support of people like you and our sponsors:

Follow Ups Full Thread

Topic - OPT transformer impedance choices? - Curly Woods 15:30:26 01/24/07 (21)

Don't frett over output trannies, many choices available - drlowmu 19:11:33 01/25/07 (6)

With all due respect. Without a good OPT, we'll all start behind the 8 ball (nt) - KIS 20:53:08 01/25/07 (5)

To be fair, I think what Jeff's saying here . . . - Ray Moth 21:25:33 01/25/07 (4)

I have heard most of those OPT brands that Jeff is recommending . . . - KIS 06:38:27 01/26/07 (1)

Re: I have heard most of those OPT brands that Jeff is recommending . . . - Ray Moth 17:27:01 01/26/07 (0)

Re: To be fair, I think what Jeff's saying here . . . - drlowmu 00:45:03 01/26/07 (1)

Of course, you're right - Ray Moth 06:20:44 01/26/07 (0)

Buy the best quality transformer. - richardl 11:18:32 01/25/07 (3)

That is what I said: Favour the OPT - meaning smaller turn ratio (nt) - KIS 17:25:15 01/25/07 (1)

Re: That is what I said: Favour the OPT - meaning smaller turn ratio (nt) - dave slagle 11:29:40 01/26/07 (0)

Fully agree, the OPT is the single most critical part. - Ray Moth 14:35:14 01/25/07 (0)

IMHO - Russ57 15:53:43 01/24/07 (9)

I read most of your posts, and find you to be very knowledgeable ... - KIS 18:39:51 01/24/07 (8)

Re: one thing to look at - Mahatma Kane Jeeves 06:07:43 01/25/07 (2)

Re: one thing to look at - mqracing 20:21:58 01/25/07 (1)

Re: one thing to look at - Mahatma Kane Jeeves 05:16:51 01/28/07 (0)

Great answers below - Russ57 05:11:02 01/25/07 (2)

Re: Great answers below - Curly Woods 06:05:53 01/25/07 (1)

If your speakers are only 88dB . . . - Ray Moth 07:24:26 01/25/07 (0)

Re: I read most of your posts, and find you to be very knowledgeable ... - Ray Moth 23:33:55 01/24/07 (0)

Re: I read most of your posts, and find you to be very knowledgeable ... - Gingertube 19:52:19 01/24/07 (0)

Follow Ups

Re: I read most of your posts, and find you to be very knowledgeable ... - Gingertube 19:52:19 01/24/07 (0)

You can not post to an archived thread.