I want to see what their impedance ratios are - and seems like I have some mistake in my calculations that gives me wrong results every time. I know I'm an idiot but I still want to know.

Here's what I'm doing - where the mistake is?

1. I feed the primary of the SE OT with 40VAC from a variac.

2. I measure the secondary voltage.

3. I'm not sure already, but since impedance ratio = voltage ratio squared, I calculate it that way.

For example:

a SE OT from a reel to reel. The power tube was ECL82, speaker - 8 ohm, power transformer has 235VAC secondary (around 250V B+). ECL 82's datasheet says 8K load for 3.5W output.

So my measuremenst go like this: 40VAC on the primary, measured 0.6VAC on the secondary.

Z = (40/0.6)squared = 66.6666squared = 4444.44

With 8 ohm speaker it must be 4444 X 8 = 35.5K primary.

Makes sence? NO!!!

Another SE OT, from a radio which had 7C5 tube. must be 5K.

40VAC primary - 0.5VAC secondary.

Z=6400. With the 8ohm speaker it should have been 51.2K primary.

etc. etc.