We wanted to get a good representation of the frequency response of the new Mullard 5-10 output transformer, so we hooked up the setup shown in the schematic below:
An audio oscillator is used to drive a lab amp, that has a 17V RMS outpur way above the expected frequency range of the transformer under test. A 6K6 series resistor is used to simulate the anode resistance of the two output valves. A non inductive load is attached to the secondary.
The response is constructed by setting the oscillator to the required frequency, the output of the amp is set to a known amplitude, that you will be able to keep constant, in our case this was 15V RMS, or 42.4V Pk-Pk.
At each frequency the amplitude at the amplifiers output is adjusted to the set point, and a measure of the amplitude on the secondary is taken.
I used a Pico scope with true RMS measurements, and some averaging to get a good reading of the input voltage and the output voltage.
Using Excel I was able to plot the response of the transformer, relative to the level at 1KHz, which is taken as the 0dB point
As can be seen the response is very good indeed. The -1dB points being taken as 4Hz and 60KHz.
The measured leakage inductance was measured as 5.5mH,
So we are very pleased with the results. It is an excellent transformer, and is now available here.