I found an old OPT & did some calculations to work out the Impedance.

I worked this out using a frequency of 500Hz about mid range for the Guitar signal.

Primary side first:

L = 14.9H, DC resistance is 805 Ohms

XL = 2pi f L

= 6.28 X 500 X 14.9

= 46,786 Ohms

ZL = sqrt R^2 + XL^2

= 14,797 Ohms

Secondry side:

L = 3mH DC Resistance is .6 Ohms

XL = 2pi f L

= 6.28 X 500 X .003

= 9.42 Ohms

ZL = sqrt R^2 + XL^2

= 9.4 Ohms

My question is that of course that ZL changes with frequency so at what frequency should we work out these figures.

By choosing the approx mid range of the guitar frequencies 500Hz, did I in fact do the correct thing.

The thing that bothers me is that some of the harmonics --- overtone frequencies from guitars are a lot higher than the fundamental string frequencies.

What bearing has the output transformers of tube amps actually have on these overtone frequencies.

It would seem it could actually make or break a truly great guitar & or Guitar amplifier?

Cheers