Ultra linear transformers for guitar amp build HELP!!

[diydidi]

Hi
I recently acquired some output transformers from a guy that's immigrating.
I have attached some pics. There is no recognisable manufacturer name on any of them. I was told be the guy his late father used them, but he didn't know much about the specs.They are ultra linear type, with the screen taps 20% to the centre tap.
I have attached some pics.
We measured the winding ratio to be 55 to the outer-most primary pins. This gave us a total primary impedance ±12100 with a 4ohm sec.
Does anyone what these might have been used for and if it's possible to build a 18W guitar amp with EL84's.?
Any input will be appreciated.
Thanx

[J M Fahey]

They look reasonable, and I'd say: breadboard one 18W amp and try it.
I guess it will work fine (although don't sweat to get real 18W RMS, I'd expect some 12W RMS or so, still plenty) .
If they work well, now you can build a dozen "18W" heads or combo which you will easily sell in a short time.
At least I would

[trobbins]

Do the DCR of the primary winding, and the core size compare to similar OT's ?

When you measured the voltage ratio, did you apply voltage to one-half of the primary, and then use the measured voltage on the other half for the turns calculations, as just using the applied voltage for turns calculations can give a bit of error.

[diydidi]

Hi
I applied an ac voltage to the sec and measured primary. This gave me the voltage/ turns ratio. In both cases i measured the primary and sec voltages just incase my source might get "loaded" down.

[trobbins]

You may have introduced some error by applying the voltage source to the secondary, but it only affects accuracy of turns ratio - which is not really the issue here.

[Tom Phillips]

You may have introduced some error by applying the voltage source to the secondary, but it only affects accuracy of turns ratio - which is not really the issue here.

I don't understand your concern. Especially since diydidi verified the actual voltage applied to eliminate loading effects. Secondary and primary designations are relative and the transformer doesn't care which "direction" the voltage is transformed. Correct?

[trobbins]

The driving signal was applied to the single secondary winding. There is no other secondary winding. Depending on the applied voltage, there is a certain level of excitation current passing in that winding. Measuring the voltage on the secondary winding includes the effects of any current flowing, which may cause some inaccuracy in determining turns ratio.

The somewhat harder way to do the test is to apply a higher voltage to one of the primary half-windings, and then measure the voltage generated on the other primary half-winding and use it for the primary turns reference. But a good meter is needed to then measure the secondary voltage, as it will be a much lower level.

[trem]

12k primary.?
Isn't that about what a pair of those old 6K6 power tubes like to see.?