Figuring out proper speaker load for single ended 7591 amp

[Bob Opera]

I'd like to figure out the ideal speaker load for an amp powered by a single 7591A tube (Premier Twin 8) running at 320VDC.
I fed the output transformer 10VAC and got 0.48VAC out of the secondary, so it appears to have a 20:1 winding ratio.
Can you help me with the math please?

[Jazz P Bass]

You have to know what the manufactures information is on the plate load resistance.
And you get that by looking at the tube data sheet.
http://www.mif.pg.gda.pl/homepages/f...168/7/7591.pdf
In the case of the 7591 beam tube, it is listed as 3000 ohms.
So, knowing the Turns Ratio, we can calculate the impedance ratio of the unknown transformer and the impedance in a given load to the secondary.
The impedance ratio is the square of the turns ratio: in your example, 20 x 20 = 400.
That means an impedance ratio of 400:1
Then you multiply the impedance ratio by the expected load impedance.
So in a given load impedance of 8 ohms the transformer impedance is 8 X 400 = 3200 ohms.
An 8 ohm speaker would fit the bill.

[Amp Kat]

Heres a link that kinda explains what ^^^ Jazz just said but agree you have to know some specs and frequency can have an effect too.

Output Transformer Impedance

[Bob Opera]

Thanks for your replies.

In looking at the 7591 data sheet, isn't the load resistance actually 3000 ohms for class A/ single ended amps?

[Jazz P Bass]

OOps!
See, your learning
3K it is, Class A, single ended.

[Bob Opera]

Last question: In a less than ideal world, if you had to go with two eight ohm speakers would you wire them in parallel or in series?