travler: RF transformer repair may be easy

ID: 202262
travler: RF transformer repair may be easy 
13.Oct.09 02:59
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Joe Sousa (USA)
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Joe Sousa

Hello Radiophiles,

Ross Hoff has posted a useful method to work around an open untuned RF transformer primary. Ross made his repair on a Crosley 127 Superhet.

As Konrad Birkner points out in his reply to Ross, the ideal approach would be actual replacement of the transformer.

Sometimes, a replacement can't be found.

I had good luck repairing the two open untuned transformers transformers in my Silvertone Trav-ler portable radio.

Part of what made the repair easy is that the exact number of turns is of no importance because the transformers are not tuned. The other aspect that made this repair easy is that the number of turns is not too large.

Often the fault is corrosion right at the coil wire solder connection. I have fixed a few audio and RF transformer just by resoldering the end wires.

The two transformers of the Travler were open and had opens in the middle of the winding that were caused by corrosion. I found the open spots, added a similar ammount of fine wire, and got the transformers working again.

In my case the RF transformers offered a modest amount of step-up gain around 1.3X per transformer.

The transformer load also eliminates plate resistor drop, which reduces plate voltage on a triode and therefor, it's transconductance. This is particularly important if the plate supply is a modest 90V.

click to enlarge photos

The second transformer shown on the right has a wood core, and only need to have the internal wires reconnected. They had corroded open at the point where they exit the transformer.

Regards,

-Joe

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