Eddystone EC10
Written by Bryce Ringwood   

The Eddystone EC10 was one of Stratton and Company's early transistor radios. I don't have the set any more, so the only photo of it I can provide is the one on this 1968 advertisement. This is not too clear and there are better photos elsewhere on the Internet.
 

Transistors: 

OC171 RF Stage
OC171 Mixer
OC171 Osc
OC171 IF
OC171 BFO
OC 71 Audio
OC 83 Audio

(Subject to confirmation - I'm faily certain my set had different transistors!)

Controls
 

RF Gain
AF Gain
BFO Pitch
Wavechange (5 Bands)
Tuning

Dial Lights
CW Filter
AGC
BFO


Phone Jack
 

ec10 advert jan1968sml

Review

The problem that the designers faced with this set was simply that the transistors of the time were not up to the performance of valves. In an effort to squeeze as much sensitivity as possible from the OC171 RF stage, the designers used a “grounded base configuration”. This configuration loads the input coils and reduces their “Q” (A measure of quality of the inductance), this lowers the tuned circuit gain and increases the front-end bandwidth.

The bottom line is that this radio suffered from lack of sensitivity and image problems. For example, suppose a radio is tuned to 21.470 MHz, and the local oscillator runs above the signal frequency – then it will run at 21.470+.465 = 21,93 MHz. Unfortunately, the same station will also be heard when the local oscillator is tuned to 21.470-.465=21.005 MHz. This corresponds to 21.470-.465=20.535 MHz on the tuning dial at somewhat reduced strength because the RF circuitry is insufficiently selective to remove the so-called “image”.

Another problem was that the AGC action was insufficiently strong and this made the set prone to overloading. This problem persisted with many later radios, and many simply won't work on anything other than a short whip antenna. I never really had much of a problem with this, because at the time I only used the EC10 with a short indoor antenna.

For me the problem with the set was lack of selectivity, but in this case the problem was me, not the radio. The set was designed to provide reasonable audio quality, and so deliberately had fairly broad selectivity. It was very heavy = expnsive on batteries.

All this sounds rather gloomy, but it was portable, robust and perfectly adequate for short wave listening. I traded mine in for another Eddystone, but as the new set was VHF only, I soon missed shortwave. In addition, I had applied to emigrate to South Africa and wanted a set that would receive “Radio South Africa” (as it was then). I had no money, but I had a fairly good junk box which included an Eddystone 898 dial drive and so resolved to make my own version of the EC10. This was  before the Barlow Wadley became available in the UK.

The Home Made Replacement

Of course, 40-odd years ago, I didn't have a computer, nor did I have all the required skills, if truth be known. I also only had a 3-gang 265 pf capacitor that I had picked up as a sale item. Home Radio with Eddystone 898 DialThis restricted the medium wave coverage. The end result was a home made version of the EC10, with all of its vices, even down to the high battery consumption, but at least it was a short-wave radio and it worked and still does. It uses FETs in the front end and in some of the IF amplifier stages, which makes it a little more sensitive than the EC10 and it has a product detector, making it somewhat better for SSB reception. Shortly after arriving in South Africa, it got a mechanical filter, so that it is much more selective than the EC10, at the expense of audio quality. (I tried a 16kHz wide ferrite filter, but it made for weird audio – like everyone was breathing helium. Indescribable.) Trying out the radio today, I managed to receive DX on 29.499 MHz. (SSB) Maybe slightly less readable than my main receiver, but it still works well. Its my tribute to the EC10.

 
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