REDUX: FA: Pair New Heyboer 40W SE Output Transformers



Hi Jon,

Thanks for making the measurements for me. If your measurements are
accurate, then my interpretation of this data is that the best thing to
do with this transformer is to "bin" it. The turns ratio, ignoring the
effects of winding resistance, implies an end to end secondary impedance
of approximately 18.95 Ohms. A secondary DC resistance 10.0 Ohms is
totally unreasonable, nearly an order of magnitude greater than what you
would like to see. Given the turns ratio and the DC resistances, it
appears that the secondary is wound from finer wire than the primary,
which is sort of backwards, although the "spec." *** implied that the
secondary was wound of fine wire. One has to really wonder what this
transformer was originally designed for, certainly not driving a
loudspeaker. The only additional test I would make would be to verify
that the secondary winding does not use much heavier wire at one end
than the other which might change my interpretation of the data. I
would do this by again applying 6.3 volts across the full secondary and
measuring the voltage at each tap to find the tap closest to the center
which would have approximately 3.15 volts on it. I would then measure
the DC resistance between this tap and each end of the secondary
winding. If one of these resistances was say 0.5 Ohms or less, then the
transformer could have some use other than a trip to the "bin".


Regards,

John Byrns


John,

Doug Bannard kindly pointed out that an ESR meter is a bad way to measure DC
resistance with something that has a much reactance as an output
transformer.

My measurements on the secondary DC resistance for the tranny was plain
wrong.

I measured again with my VOM, and got 0.5 - 0.6 ohms on the secondary. I
then compared with a 1.6 ohm resistor and measured 1.7 ohms.

Next, I connected the transformer secondary in series with a 100 ohm 1%
resistor.

Using a regulated power supply, I dialed up 10 volts DC.

I then measured the voltage across the secondary (40.6 mV) which corresponds
to 4 ma of current, which works out to about .4 ohms, which is in lie with
the VOM meter.

If so, it doesn't seem like a bin item to me.

Sorry for the confusion.

Jon



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