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Identify giant transformer from 1978 tape reel

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MarkF:
Getting closer.  Only missing brown wire.
https://elektrotanya.com/pioneer_rt-701_rt-707_art2540_additional.pdf/download.html#dl

   

Richard Crowley:
It is trivial to measure the other two wires.  As suggested by @MarkF, chances are excellent that they are primary (input) voltage taps for different international mains voltages.  In any case, the info for the secondary (output) windings seems quite reliable.

MarkF:
I believe the primary is one of two configurations.
You will need to put the multimeter on the four wires to see if there are two windings or one winding with two center taps.

   

ArthurDent:
MarkF -
--- Quote ---"I believe the primary is one of two configurations."
--- End quote ---

There is one other possibility but not as likely. If you ring out the wires and find one that doesn't seem to be connected to any other winding, it could be an electrostatic shield between primary and secondaries. Some times the shield is brought out as a separate lead although the shield lead is often just connected to the metal core. 

One big advantage of finding the 2 manuals with schematics is that you might have a better idea what the current rating of each winding is. The power consumption is stated to be 120 watts so at the 120 VAC input shown, that would be around 1 A and the input fuse is 2 A. If the fuses in the secondaries are also about the 2:1 ratio then you can guess that the current for the secondaries is half the fuse rating for that winding. You can double check by adding the measured secondary voltages times their current guess and see if the total is close to the 120 watt total consumption. 

Most equipment doesn't have all the secondaries fused like this unit and without that information you wouldn't know any of the currents on the multiple windings. This would be the same as if you used a meter figured out the  primary winding and test powered it through a lamp to make sure then measured the secondary voltages. You know the voltage on each winding but you have no idea the current rating of each winding.

If you take the end shells off the transformer and can see where the solid wire comes from the bobbin you can make an estimate by looking at the relative wire sizes. If I recall years ago when I wound some transformers there was some constant, perhaps between 750 and 1000 that you divided the circular mils of the wire by to get an estimate of current.

Fun exercise to try to figure it out and I've saved a lot of similar transformers but it is much better if the transformer you find has the rating printed on the transformer!

Cubdriver:

--- Quote from: MarkF on May 03, 2019, 11:32:42 pm ---Getting closer.  Only missing brown wire.
https://elektrotanya.com/pioneer_rt-701_rt-707_art2540_additional.pdf/download.html#dl

   

--- End quote ---

Given that electrotanya schematic, my guess would be that the brown wire might be the 120V primary tap - check to see if it has continuity with the black, violet and grey wires.  If that is correct, the resistance between the black and grey will be highest, black and violet less, and black and brow the least of the three.

-Pat

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