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Eico HF20 Output Txr Questions

Doug R

2007-10-10 6:21 pm
Hi All,
I have been going through some transformers that I will never get around to using so I can send them on their way to someone who can get some use out of them.

I have the power and output transformers from an Eico HF20 push-pull amp that was working before I pulled the transformers. My question is about the output transformer, which is HUGE! It is potted, weighs over 13 pounds and is the size of a cantaloupe.

There are six primary leads. Five have the braided cover that has gotten so discolored that I can't tell which color is which. The sixth wire is plastic coated and definitely brown. The txr is potted, and it doesn't appear that anyone has been inside to change the lead wire.

I measured the resistances of the leads and find they differ somewhat from what Eico shows on their schematic. See the illustration for values. In case it is hard to read, Eico shows 60 ohms from Center to UL, then 90 ohms from UL to plate lead (brown or blue.) I get 50 and 75 ohms for one winding and 52 and 62 ohms for the other. There is no common CT, each winding has an independent lead for red (if I could tell which was red.) Again, see the illustration from the schematic.

Two questions:
(1) Are these ohm values OK?
(2) Did Eico typically use a wire with different insulation for the brown lead for some reason?

Thanks for any help you can offer.


  • Eico ohm values.jpg
    Eico ohm values.jpg
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It IS normal for the halves of a P-P transformer to have different resistance, since they have equal numbers of turns but UNEQUAL length (outer layers ar longer than inner ones). Without know the layer arrangement of this transformer, I can't say if they're normal, (but probably are...). What matters is tuns ratio, which determines impedance ratio. As far as the one plastic-insulated wire, it's probably what the transformer maker had in stock...