Primary impedance of original jtm 45 ot?

[neskor]

If I apply 400hz AC signal 1V RMS on secondary, on primary I'm getting 26.65V RMS, so it should be OK with 6.5K/8R relation

[neskor]

If put all the results in this online calculator step-down ratio looks OK
https://www.hagtech.com/loading.html

[bepone]

With 1Khz C settings and from Ub+ to secondaries I'm getting 1440pF
If I apply 400hz AC signal 1V RMS on secondary, on primary I'm getting 26.65V RMS, so it should be OK with 6.5K/8R relation

ok this is fine

If I apply 400hz AC signal 1V RMS on secondary, on primary I'm getting 26.65V RMS, so it should be OK with 6.5K/8R relation

if you get 28.65 then is ok, 28.65*28.65*8=6k5..
but ill try also this method today

[pdf64]

Have you checked the high frequency to ultrasonic frequency and phase response of your’s?
Mine has a weird resonant peak and phase shift around 40kHz.

I didn't
I don't have balanced signal generator, maybe runing the secondary with SG and solid state amp will work, but never tried.
I think the only valid measurments will be if we put OT in the circuit.

I don’t see that a balanced sig gen (or excitation driver) is needed to check an OT’s response, ie when connecting to the primary.
That can be verified by comparing the results to the response at the primary when driving the secondary.

The response in circuit will be affected the the other contributory factors involved with the amp’s open and closed loop performance.

Though the resonance I mentioned previously was evident when checking the OT with a sig gen and scope, or in the amp circuit open loop response.
Closed loop, presence at minimum, the circuit was unstable at around the OT resonant frequency.