What is the result of higher impedance in SET?

The 8 Ohm-only secondary might be a problem: tough to match the impedance of most speakers which can go down to 2 or 3 ohms for a lot of frequencies. But the higher primary impedance does have benefits: lower overall THD and the ability to handle wider speaker impedance swings. But, there's a reason why the transformer primary impedance is matched with the triode plate resistance: for maximum power transfer to the xfmr and the speakers. For SET's, with their meager power to begin with, preserving that power is usually the primary concern.

The most you want the xfmr Zp to go above the plate resistance is a factor of two, so you can get away with using it on the 245. The result will be less volume at a given pot setting.

For the 2A3 and 300B, not recommended. The power transfer is reduced too much to effectively operate. They're 3.5 and 8 watts, respectively, and any decrease in power will affect your system's performance.

Gs, Is it possible to shunt the transformer's impedance with resistor?
What will be the result?

The second option is that Mercury Magnetics produce transformers for any Zp and Zs specified.

Direct with feedback?

Do you know any good book or web resource on SET design (specific to 300B, 245, 2A3) for amateur DIYers? Not just here is the schematic, now go build it; but explaining each amplification stages and calculation of output, etc.

Hi:

How much do you know about basic electricity?

An old (pre1960) ARRL (American Radio Relay League) Handbook is a good place to start if you are new to tube-electronics and have basic Q's about how things like transformers work. Can be had on ebay for about $10-15.

I have a fairly large collection of DIY tube sites fairly organized w/ live links in Word format. One part of it is a collection of sites I think would be helpful for beginners. It also includes a list of about twenty online articles about audio transformers you might find helpful (several very good for the basics) given your question. It would at least be a helpful place to start. Drop me an email if you would llike a copy.(I cannot send it through agon e-mail because it won't take an attachment) Some of the books I have found useful are listed in the outline.

Here is a simple article on OPTs that explains some of the design tradeoffs. http://www.aikenamps.com/OutputTransformers.html

Cheers
I remain

Thanks, Clueless. I forwarded my email to you.