[Ed Kraushar]

I picked up a 1926 Stromberg Carlson 601A Neutrodyne battery radio at a radio club auction some time
ago. This radio model is notorious for two broken pot metal gears on the tuning capacitor shafts. It sat in the
shop a long time while I explored the options for replacing the gears. It is easy to let these hard jobs slide.

I had read that new brass gears could be found but that the 5 inch diameter gears were expensive, probably
costing more than the radio is worth. One website recommended plastic gears but ones available were not
large enough in diameter. The other problem is that I live in the country where resources are limited so I
decided to try a fix using readily available materials. This is the result.

The tuning cap on the right hand side of the radio is a three section one and fairly stiff so that the repair
must be a strong one. The one on the left hand side has only a single section. I had heard of "O" rings
being used but was not sure if they would be strong enough. I settled on a vacuum cleaner belts as they
were very strong with a cross section of almost 1/4 inch. With proper tension the small gear on the knob
shaft would dig in enough to turn the belt without slipping. Pulleys were cut from 1/4 inch plastic using a
fly cutter in a drill press. If I was doing it again I would use a little thicker plastic. The pulleys were
temporarily mounted on a bolt so that they could be spun while a round file was held against their perimeter
to cut a "U" channel in their edge for the belt to run in. The diameter of the pulley was determined by the
diameter of the belt less enough to allow the belt to run around the gear with a fair tension.

To fasten the pulley to the capacitor shaft I used 1/2 inch diameter hex head bolts. These were drilled out
along their length with a 5/16 inch hole to fit over the tuning capacitor shaft. The hex head is large enough
to be drilled through from the side and tapped to accept a 6×32 set screw to hold the assembly in place. To
hold the pulley on the bolt a fender washer was brazed to the bolt and the pulley drilled out to fit on the
bolt. It is fastened to the fender washer with a couple of screws. The bolt was cut to the proper length to fit
the shaft.

Rear view of the assembly.

This repair although not authentic works very well.

The additional work required was restuffing eight capacitor cans with 1 mfd caps and the rewinding of two
of the three audio interstage transformers as they were open. The iron frame makes this a very heavy radio.

The original finish was quite good so it was cleaned up and waxed with a dark tinted wax.

Ed.

[Gerry O’Hara]

Very nice-looking radio Ed and a great improvisation for that pesky pot metal gear!

[Ed Kraushar]

Gerry O’Hara wrote:

Very nice-looking radio Ed and a great improvisation for that pesky pot metal gear!

Thanks Gerry. What appealed to me about this fix other than the very low cost is that the basic radio is not changed. If a future owner wishes to use the brass gears, (still not original), my pulleys can be slipped off and gears put on the shafts.

Ed.

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