Testing the frequency response of a TXOP OOOO1 output transformer

[Yosser]

I would like to test the frequency response of the above to see it it would be suitable for use in a tube hi-fi amplifier.
There are sweep generator and spectrum analyzer apps which work with a pc sound card and may help to do this.
Has anybody done this, if so, I would like some advice?
Some people insist that tube guitar amplifier output transformers are substandard because guitars have nothing above 5K and are therefore built to a cost and not to a specification
I don't believe that as quality guitar amplifier output transformers a multilayered as stability is also required.
A test would help to clarify these thoughts.

[pdf64]

I've used a scope and sig gen to check the amplitude-phase-frequency linearity of a few OTs.
Hammond provide bode plots on some of their OT model info.

If doing it yourself, the test signal power level, source impedance and load resistance are variables you'd need to consider.

[Yosser]

I've used a scope and sig gen to check the amplitude-phase-frequency linearity of a few OTs.
Hammond provide bode plots on some of their OT model info.

If doing it yourself, the test signal power level, source impedance and load resistance are variables you'd need to consider.

These where the criteria was hoping to get some help on.
Can you advise me?
my proposed gear would be pc software sweep generator, an external sound card, domestic ss hifi amplifier at 500mw the transformer  and 8 ohm load on the secondary
I would then record the output and analyse it with pc software.

[pdf64]

Are you hoping to test the bass response at high power?
If so you'll need much more test amp power than 1/2W.
Are you planning to include the effect of the anode resistance of the output valves on the OT frequency response?
If so you'll need a series resistor.
As a guideline, the resistor should be about equal to the primary impedance if it's a triode or UL output, perhaps 2 to 3x the primary impedance if it's pentode.
Obviously, if you're pushing high power, the resistor will need to be suitably rated, and the resistor will make the test amp power output requirement even higher.

My experience of test software is that it typically has a steep learning curve, so don't expect good results quickly.

[Merlin]

What pdf said. Transformer frequency response changes drastically depending on the source and load impedances used, so you need to think about what it is you're trying to test.
If you want to test the transformer at a reasonable power level a quick and dirty way is to use a power amplifier and run the transformer backwards, e.g. 2.8V into the 8 ohm tap would be 1W.
The primary (which is now the secondary) should be loaded with the transformer rated primary impedance, so this example shows a 5k transformer being tested.
A divider drops the voltage down to something suitable for your measuring instrument.
You can also add a resistor to simulate source impedance, remembering that it must be scaled down by the impedance ratio, since the transformer is backwards. For example, a pair of power pentodes might have an effective internal resistance of about 40k/2 = 20k, so you would use a 8/5000 * 20000 = 32 ohm resistor (33 ohm, 5 watts would do).

But the most realistic option is to build an actual tube output stage (as clean as possible) and run the transformer as intended.

[acheld]

Having built several "HiFi" power amps using both Edcor and Hammond OT's, I'd say skip the test and just build.  What matters is what you actually hear in a real life situation, and these companies make good product. 

It is probably true that an appropriately chosen Lundahl OT is "better" than an Edcor or Hammond, but for me and my family we are not hearing a big difference.

It can be fun testing, but as Merlin and PDF have alluded to, it is technically challenging to do right.