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T.R.F. RADIOS - PART 4 - including The Medium Wave Mini    T.R.F. RADIOS PART 5   TRF RADIOS - PART 6

Rosha and Daniel's 'Ladybird' Radio - continued - more photographs:

Hi, I finally managed to make my own Ladybird Radio in Iran. I bought that book [Making A Transistor Radio] in winter 1987. My last attempt was not successful because of mistakes in the third transistor connecting and some other faults. Since I didn’t find any “OC” transistors, I used a Japanese IF Amp transistor (2SA49) instead of OC45. It was acceptable. Other transistors such ac AF117 (General Tr.)  and AF126 (FM  IF  Tr.) didn’t  work.

All of Japanese 2SB series could be used. I  had some 2SB56, 2SB175 and 2SB376.  .

Because I  couldn’t find a radio frequency choke (r.f.c.) I used a Long Wave Coil [This would be of similar inductance]. Unfortunately my 9 volt battery was dead, so I connected a 9 volt DC power supply. My the only problem is noise.

I made some radios but I feel real satisfaction this time! Last night when I was ready to switch it on, my four year old son, Daniel, said to me: “Will you give it to me if it works this time?” ...and he owned it!

Update April 2011:
I have taken some photographs, as you see the radio works with germainium diodes OA79 and IN60 - obviously silicon diodes such as 1N4148 cannot be used.

I bought a tatty PHILIPS radio for just  $2.00 with the intention of breaking it for spares, but I repaired it and replaced my 2SA49 in the Ladybird radio with a Mullard OC45 (hilips I.F. stage). But I still use Japanese one and no re-alignment was necessary.

My radio (It is better to say Daniel’s one!) has 2 trimmers and a power indicator LED. When I connect a 9 volt adapter, the third transistor (2SB376 or 2SB75) warms up - so it is better to use lower ranges such as 7.5V .Connecting a 9V battery, noise will be reduced. I admit that I didn’t spend much time making it’s box.

Thank you very much for your help and advice.

Best regards,

Rosha

Henry's very useful related web page highlights some technical pitfalls and solutions to problems that may be encountered along the way. It also explains why substituting alternative "equivalent" transistors may not work. For example there seems to be no suitable alternative to the OC45 in the RF section in this particular circuit configuration. While the OC71 could be subsituted for an OC81, for example, but still needs a small modification to the emitter circuit. For example if substituting the first OC71 with an OC81 then it will be necessary to connect a 1k Ohm emitter resistor in parallel with a 22uF bypass capacitor to ground, rather than a direct connection to ground. This will stabilise the d.c. operating point while maintaining the audio gain.