Re: Ping Patrick (was Re: FA: Pair New Heyboer 40W SE OutputTransformers



Jon Yaeger wrote:

I am in the planning stages of another funky amplifier project, these
transformers look like they might just be weird enough to be at home in
the project. Would it be possible for you to make some simple
measurements on the transformer? I am curious what the end to end DC
resistance of the secondary is, as well as what the DC resistance of the
primary is. Also the primary to the entire secondary turns ratio, which
can be measured by applying 6.3 VAC @ 60 Hz across the entire secondary
winding and measuring the voltage that appears on the primary, along
with the exact voltage applied to the secondary.


Regards,

John Byrns

John,

My digital VOM is notoriously unreliable in the very low ohms range, and so
I used an ESR meter to measure the resistance of the secondary, end-to-end,
from the common lead to the 16 ohm lead.

I measured the resistance of the primary with the digital VOM, because it
was too high a resistance for the ESR meter . . . . ;-)

Both the ESR and VOM were spot-on measuring a precision 10 ohm resistor, so
I feel pretty good about the overall and relative accuracy.

I measured the input (secondary) voltage under load, and the resultant
primary voltage with no load.

Here are the results:

Primary resistance: 47.2 ohms

Secondary resistance: 10.0 ohms
(end-to-end)

Input (secondary voltage) 6.32 VAC

Output (primary voltage) 72.60 VAC

Voltage / turns ratio: 11.5

I'm curious what your interpretation of this data might be.

I've got the jig still set up if you have other questions.

Thanks.

Jon

Your transformer has a P:S turn ratio of 11.5:1.

This means the impedance ratio is 11.5 x 11.5 or 132.3:1.

If the primary has 47 ohms dcr, then the primary load should be 20 times
this value, ie, about 940 ohms minimum.

Therefore the secondary load would be 940/132 = 7.12 ohms.

It also could match from 2,500 ohms to 2,500/132 = 18.9 ohms.

or 2,117 ohms to 16 ohms.

But you say your transformer has a secondary with 10 ohms dcr.
This seems way too high a resistance value for a speaker secondary,
because the winding resistance should always be less than 5% of the load
value connected.
The winding resistance in effect appears as series resistance to the
load.
5% of winding resistance in P and S windings give winding losses of 10%
total,
so that if the tranny has 25 watts input, there is only 22.5 watts
available at the output
and 2.5 watts of power ie heat is generated and wasted in the
transformer.


For any load connected betaeen say 8 and 20 ohms, the sec dcr should be
less than 0.5 ohms,
and not the very high 10 ohms you say you measured.

To accurately measure low resistances, connect a battery of say 6Vdc to
a known 10 ohm R
in series with the winding you are measuring.
measure the dc voltage across the 10 ohm R, and across the winding you
want to measure.

This will give you the current flow so that from Ohm's Law
the unknown winding resistance = Vdc across coil / Idc through coil.

Patrick Turner.
.

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