[GuentherParticipant]

In the HOBBY magazine of August 1966 a story about the new Lectron System (Electronic Dominoes) showed some samples how to use. Across two pages 15 Lectron blocks could be seen from which 4 blocks are appears to be “strange”  – can you discover these?

Even the remark “In Entwicklung befinden sich noch Bausteine mit bereits abgeglichenen Zwischenfrequenzstufen usw.” (English: Modules with already adjusted intermediate frequency stages etc. are still under development) – see the magnified text down left.

That gave me the opportunity to introduce my version of an AM BC receiver. The very first time these circuits were used was November 1954 (Regency TR-1 pocket receiver, the first “real” transistor radio with a special developed set of transistors made by Texas Instruments and built by I.D.E.A. – as a worldwide success story!

For the AF amplification I used a complementary push-pull output stage with the special transistor pair of OC74 (pnp) and OC140 (npn) – very new because in Europe no npn Germanium transistors were common!

This kind of circuits were used by Philips from 1960 to 1963 with big success and allowed good reception results.

The second important usage of this circuit for me is the possibility to check nearly every part of unknown,  dismantled or removed parts from radios, e.g. IF filters. If they are able and – if so – to adjust the ferrit core to the right IF frequency of 455 kHz / kcps. If successful I could use these tested parts to build new radios or use these for repair, because that are the most critical parts.

To check the IF filters, I am using a Lectron block with wires, solder the unknown coil /filter and insert it into the above circuit.

This superhet does not make use of the reflex technique – the folling circuit does – it was used by the German REX Bambinetta / Rexetta models – and with other schematics from many other manufacturers in nearly all countries, most of them used an AF transformer to “split” between IF and AF. In this circuit the IF stage is used twice: after AM detection the AF signal was amplified in this transistor, too.

To save additional (and unnecessary) connections I am using modified potentiometer blocks, see above.

The BC oscillator/mixer tuning block is built once and suitable adjusted. Then they can be used for nearly every BC receiver. The pnp Germanium transistor has a socket, so I may change it by plug in a npn Silicon transistor for use in complete npn circuits 🙂

Articles with ZN414, Silicon npn (reflex stage) and special SW (Shortwave) receivers and a superhet will follow soon.

Best,

G.

• This topic was modified 5 years ago by Guenther.
• This topic was modified 5 years ago by Michael. Reason: Changed font and size styling for easier reading

[LectronFanModerator]

Hello Guenther,

This is amazing ! What an impressive radio circuits. I never got my superhets working properly.

I even got a few very old AM pocket radios with 2 IF circuits,  but I never succeed to align these properly. And the alignment of the oscillator section is even worse !

But I like your Lectron setup. Maybe I will give this also a try …

Greetings

• This reply was modified 5 years ago by Michael. Reason: Changed font and size styling for easier reading

[MichaelKeymaster]

Hi Guenther,

The ‘strange blocks’ that I observe are (from left to right) numbers 10, 11, 14 and 15.  How did I do?

I don’t believe that I have this article, I will have to check my archives.  Very nice discovery Guenther!  Thank you for sharing this.

Best,
Michael

[GuentherParticipant]

Hi Michael,

… not so bad! To be honest: we can count 5 non-standard blocks:

#3 = potentiometer without embossed value (it must be 10kΩ, part #8043) – we know that many early blocks had no markings

#10 = measure block, part #8058  – here the prototype with a 4mm “telephone socket” like the large demonstration blocks 81 x 81 mm

#11 = part #8044, the series version had the value “220Ω” above the resistor, beneath: “2x 100µF”

#14 = the LDR block #8048 is clear, with a tiny hole in the white cover. Normal: black housing, oval hole

#15 = RC combination 120Ω + 100µF, part #8056, was NEVER in any set or catalog (only adverts of Braun)

You got 90 points (of 100)    😉

Best,

G.

• This reply was modified 5 years ago by Michael. Reason: Changed font and size styling for easier reading

[MichaelKeymaster]

Hi Guenther,

Thank you for the passing grade, 🙂 .  Still, you said to point out four and I did.  Adding a 5th block after the fact is not quite fair!

Oh well, fun game anyway, thanks!

Best,
M.

[Author]

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