This must be the jewel of my collection, a radio I've been after for thirty years! Made in the USSR in September 1968, the instruction leaflet claims it to be the smallest production receiver in the world, which at the time would have been true as it's smaller than the Sinclair Micromatic. The receiver is a 2-band 6 transistor "straight" TRF design, implememted using thin film components. It's totally self-contained with its own internal ferrite rod antenna and magnetic earpiece. Performance here in NW England is quite good, with strong reception of Radio 4 LW, Atlantic 252, Radio 5 Live and Liverpool's Magic 1548. The instruction leaflet points out that the radio is designed for reception of local stations only.
Looking at the circuit diagram, the ferrite rod antenna is tuned by variable capacitor C1, with the selected signal coupled into the base of TR1. TR1- 4 form an untuned RC-coupled RF amplifier followed by transistor detector TR5. TR6, wired as an emitter follower, drives the magnetic earphone. Waveband switching is accomplished by switch B1 shorting out part of the aerial winding in the medium wave position. The AGC voltage developed at the detector's base controls the gain of TR1. Being non-regenerative the circuit is stable and results in a receiver more easily used by the layman. This type of circuit was incorporated some years later in the legendary ZN414 radio IC. Anyone who's used regenerative reflex designs will know that they need skillful setting up to get the best from them. Specifications are as follows: Power supply, 1.2v NiCad or 1.5v disposable button cell; Coverage 150-408kHz LW, 525-1605kHz MW; Sensitivity 35mV/m, Battery consumption 4mA, power output 50uW. The case is glued together so I haven't a pic of the works.
The above pic shows the complete kit in it's little clamshell box. Left or right earpiece adaptors are supplied, and the box has a little plastic "capstan" for neatly stowing the earpiece lead. Unfortunately I don't have the optional charger. Incidentally, I do seem to remember identical radios advertised as the "Astrad Orion".
Another file from my old website and yes, I still have my Amsa. Please bear in mind that this piece was written in 2002.
Hi
That looks really good and knocks my Sinclair Micro 6 for six. I no longer have my original Sinclair or the Micromatic I bought to replace it. There was something about Radios and me, they worked for a a fair while but had to be played with, and experimented with, a bit like a cat and mouse, eventually it breaks.
Excellent little radio and you are lucky to have found one.
Mike
Hi
That looks really good and knocks my Sinclair Micro 6 for six. I no longer have my original Sinclair or the Micromatic I bought to replace it. There was something about Radios and me, they worked for a a fair while but had to be played with, and experimented with, a bit like a cat and mouse, eventually it breaks.Excellent little radio and you are lucky to have found one.
Mike
I managed to find a Micro 6 three years ago - fully functional. This piece includes PDFs of the instruction manual. As a youth I was always fascinated with radio circuits that could be built in matchboxes:
viewtopic.php?f=3&t=949&p=6999&hilit=sinclair+micro+6#p6999
Pete
It took me a long time to find a matchbox the Micro 6 would actually fit.
The kids in the playground did not believe that I had a radio in a matchbox. But they looked in awe as I slid the box open and revealed the little radio to demonstrate it.
I seen to remember being caught by a teacher playing with my matchbox in class and had it confiscated till the end of the day.
Mike
My, time flies 😊 Glad you're still enjoying it.
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A very interesting radio.
I would not have considered that shorting out a winding would be effective, but since each winding is resonant at a different frequency, I suppose there's no harm.
