SRR-13 Coils


A typical SRR/FRR/MRR Coil.

If you have ever perused the SRR/FRR/MRR series tech manuals, you probably noted the extensive coil data and winding section. Not many boatanchor manuals have that level of detail, and perhaps you wondered why. Fifty years after the radios went into service, we find out why.

Bob Goodrich, K7KMQ, had some problems with open coils in the RF and converter stages. He had hoped to find replacement parts, or that perhaps the coils had broken near the ends. No such luck! So he went back to first principles, built a coil winding machine, and used the manual instructions to wind replacement coils. In my opinion, he did a pretty good job. Here's his story and photos:

"Some time ago we swapped emails regarding a problem I had with a FRR-23, the problem was located and the receiver is performing very well. I had so much fun getting that FRR-23 going for W0BCF that I decided to get one for myself. The SRR-13A that I now have has open primaries in two coils in the RF stage, T-526 and T-527 (Bands 1 and 2) and one open primary in the mixer stage T-553 (Band 3). The primaries were open in the middle of the coils, almost like some corrosive chemical reaction, in some cases multiple opens."

"I rewound the coils on a home brew copy of the old Morris coil winder. I found this fellow on the web,, and was inspired to build my coil winder. It makes universal wound coils OK, but certainly not with the precision of the original coils. The coil dope I used is E6000 craft glue, it is a thick glue."


The coil winder.

"The coils were wound straight off the coil chart from the maintenance manual. Careful measurements were made as to the length of the coil and the coupling to the secondary winding. Attached are a couple pictures of the original coils. The band 3 mixer module coil is 38½ turns of 3 strand .0028" litz wire. The chart wanted 3 x .0025", 3 x .0028" from ebay was the best I could do. The band 2 coil on the second RF amp module is 96½ turns of 3 x .0028" litz. and the band 1 coil on the second RF amp is 314½ turns of .004" (38 gauge) single strand enameled copper wire.All universal wound."

"The receiver performs nicely, with 1.6 microvolts for 10 db S/N on most bands now."

Here are more images of the coils and rebuild modules: