Zenith Royal 300
Written by Bryce Ringwood   

This radio belonged to my father who brought it back to the UK after a business trip to the USA. For years he would listen to the BBC on this set until one fateful day he went on another business trip and dropped it from the gangplank of the SS Queen Mary on to the concrete below.

zenith300

Years later he gave it to me, but it resembled a baby's rattle rather than a radio. The case had very minor damage (Zenith claimed it was made of “unbreakable nylon”., but the transistors zenith300insidehad all fallen out of their sockets and the printed circuit board had cracked into five pieces. The supports for the circuit boards had all broken off.

My first thought was to make a completely new printed circuit board. This would have involved making a “brass rubbing” on to paper, filling in the tracks with black ink and photocopying the result onto transparent paper. Inspection of the board showed it had broken into flakes along the edges and these could probably be glued with epoxy. In any case, this would be the first phase of the tracing process.

The board was successfully joined, so I bridged across the broken tracks with short pieces of wire (trying to connect a broken track with solder never works.) The joints were all cleaned using solder cleaner. Next the transistors were all replaced in their sockets and power applied. I was immediately rewarded with atrocious quality audio. The problem was traced to a bad capacitor and the set reverted to its normal tinny quality.

The components of this radio are all valve-type capacitors and resistors. The tuning capacitor is air-spaced – simply a small version of the type used in a valve set. The same can be said of the volume control, which is just a small edition of the type used in valve radios. This seems to me to be a little odd, since miniature components were being made for hearing aids at that time.

The Royal 300 is a simple superhet with the following transistors: 2N194,2N193,2N516(IF),2N516(IF),2N35x3(AF)

The dial of this radio (and the Zenith Royal 1000 as well as the NC190) have the “CD” symbols on the dial. These were at 640kHz and 1240kHz to allow US citizens tune to the CONELRAD stations. The CONELRAD (Control of Electromagnetic Radiation) plan was a means of emergency broadcasting to the US public in the event of an attack by the Soviet bombers during the cold war. It was established in 1951 and replaced in 1963. The development of intercontinental ballistic missiles effectively made the plan redundant.

In 1956, mercury batteries seemed like good idea for portable transistor sets. And I once bought some. They turned out to be expensive and not much of an improvement over the normal dry cells of the period. Shortly after this “Mallory Batteries” (later Duracell) became available, but all in all this little radio wasn't too battery hungry. But see the Eddystone EC10 and my home made replacement both of these are or were very power hungry.

The cabinet style is typical of the '50s, with its black (or other colour) shiny case and shiny gold top. The controls have been hidden to make a neater and less comical appearance than its owl-eyed predecessor. It used to look OK perched next to the goldfish tank in our 1950s living room. I don't use it much anymore, but it has batteries and is ready when I am.

 
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