Improving Plug-In Coils
February 1935 Short Wave Craft

February 1935 Short Wave Craft [Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Short Wave Craft, published 1930 - 1936. All copyrights hereby acknowledged.

Before plug-in crystals were widely available for band selection in radio receivers, LC tank circuits did all the frequency discrimination heavy lifting. Accordingly, owners often had a selection of swappable inductors on-hand to enable listening to a variety of shortwave transmissions. During the time period of this article in a 1935 Short Wave Craft magazine, new "all wave" radios were hitting the showroom floors that largely mitigated the need for swapping components for the most popular frequency bands. "Short wave listening" (SWL) was a big deal back in the day since it enabled anyone without an amateur radio license to tune into conversations going on all over the world. Most were content to merely listen, but many were inspired to obtain their licenses in order to be able to transmit as well.

Here is a collection of vintage Toute La Radio issues (changed to Toute l'Electronique in 1962.

Improving Plug-In Coils

By C.W. Palmer

In describing the construction of a new receiver, a recent issue of Toute La Radio, a French magazine, included a useful kink for improving the efficiency of plug-in-coils.

By cutting partly through the base of the coil with a hack-saw, between the various pins which make contact with the socket, the length of insulation between pins is increased and the amount of insulation is reduced, both of which are desirable features.

The trick shown above will considerably reduce high frequency losses in plug-in coil forms.

Posted September 27, 2023
(updated from original post on 7/25/2017)