AM reflex receiver on 2 germanium transistors

Congratulations on your successful construction.It is unbelievable that it has such sensitivity.At my place in podlaskie it would probably be quiet.
My radio had to contain these amplification stages, with 5 or 6. It serves me as a bathroom radio.
Did you try to build the HF amplifier as a resonant amplifier - variable capacitor in parallel to L3 and tuning? It seems to me that you would increase its sensitivity even more. Robert R.

I was disappointed to see this thread, as I myself, in sometime in the early 1980s, tried to build the same radio. I remembered after this characteristic drawing of electronic components and the person of the author - Witold Kozak. The radio didn't work - probably having no skill, I overheated the germanium transistors or connected something wrong. I remember that the only source of information about electronics and schematics available to me at that time was the library in primary school (youngsters probably won't understand). Most of the few books there were by the same author and even then they seemed quite archaic. Does anyone know what his fate was? Given that the publishers were hooked on the 1950s, he's probably long dead.

Why are germanium semiconductors and not silicon semiconductors actually used?

tesla97 wrote:

Why are germanium semiconductors and not silicon semiconductors actually used?

Everything, as far as semiconductors are concerned, started with germanium. The first transistors were very fragile and the manufacturing process itself was far from perfect. Everything was improved and over time germanium was replaced by silicon. Here's the story ⬇️ how Japan started the pursuit of technology and how complicated the process was 👀

_ACeK_ wrote:

Everything, as far as semiconductors are concerned, started with germanium.

So not really... And galena? Neither germanium nor silicon, and a semiconductor it is.

Hello
I have my favourite schematics for AM two transistors in the input amplifier and then it's different amplifiers depending if the circuit for headphones or speaker.
I always did the detector on 2 diodes in a voltage doubler circuit, which on high watt headphones allowed comfortable listening even without a mcz amp.
Recently there have been a lot of publications with an interesting FM receiver circuit on a single transistor, but I am not able to say on what principle it works, it is not super-responsive and on top of that the antenna is attached to ground and is not coupled to the input of the circuit in any way, I have not done this circuit yet, I must try it in my free time.
Link
By the way, I have a question about the headphones "cristal" which passionately use in Japan for such construction, in very old times the Soviet in-ear version of such headphones cost pennies and now I find only headphones with prices > 100 PLN, the situation with the search on foreign sites for such headphones brings the same result, after all, structurally and materially these should be the cheapest headphones as in the old days.

Various tools are drawn on the cover of the book 🛠️



😎 Now a question for the younger ones below 50 years old what was that marked in green used for 🤔 For ease of reference I will add that it was used in electronics

_ACeK_ wrote:

Now the question

Soldering iron Today's question

Hello
Another throwback from the days when transistors were expensive and copper for coils was cheap
Superheterodyne radio on a single transistor, personally I never liked winding coils that exceeded 10 turns and in today's receivers there are more semiconductors than coils, sometimes none at all.

http://zpostbox.ru/superheterodyne_receiver_with_one_transistor.html

ArturAVS wrote:

_ACeK_ wrote:

Everything, as far as semiconductors are concerned, started with germanium.

So not quite... And galena? Neither germanium nor silicon, and a semiconductor it is.

And have you seen a transistor on galena ? Or on selenium ? Or on mercury ?

acctr wrote:

żarówka rtęciowa wrote:

With minor modifications, silicon transistors could be used

Probably yes, an AM radio can be made in dozens if not hundreds of ways. Here I am just presenting one particular implementation, distinguished by the fact that the design as well as the key elements date back to the 1960s. Otherwise, I would not be motivated to build and present here a receiver on silicon transistors, even made by CEMI.

Only why to load silicon as new AF426S , TG5S and TG51S at Gembara on Allegro you can buy new for 4 to 10 zł - I build myself a receiver from this book so much that this 5 transistor - with an amplifier included in the HF response and reflex so it should have even greater sensitivity.

PiotrPitucha wrote:

Recently, there have been many publications with an interesting FM receiver circuit on a single transistor, but I can not say on what principle it works, it is not superreaction and in addition the antenna is connected to ground and is in no way coupled to the input of the circuit, I have not yet done this circuit, I must try in a free moment.

The receiver from the link will not work - among other reasons, because P416 has too small ft- 40 MHz - it would not even work on UKF OIRT.
A lot of such simple receivers
They work on the synchronous detector principle - the input circuit operates at 87-108MHz and the heterodyne operates at 43.5 to 54MHz - demodulation occurs at the second harmonic of the heterodyne signal. Thus, there are several advantages here
1. Such a detector is suitable for the construction of a stereo receiver - there is no distortion from AM modulation as in a super-reaction receiver !!!!
2. We gain the sensitivity of the superheterodyne
3. You gain instant noise suppression between stations
4. we gain quasi ARC.z using emitter capacitance - it just doesn't remember whether emitter base or emitter collector.
5. No peeing into the antenna - this means that such a receiver does not interfere with frequencies in the range of 43 to 54 MHz because for these frequencies the input circuit 87-108MHz is shorted to ground - hence the presence of a 50uF capacitor in the base.
6. The disadvantage may be that the receiver only synchronises to strong stations - noise and weak stations are ignored - to receive weaker stations you would probably have to use an HF amplifier with ARW.

ATTENTION - such receivers are very popular in Russia - on Russian language websites there are also diagrams of stereo receivers, but they will not receive in stereo in Poland due to a different system of signal emission - hence their simplicity, to get stereo reception in Poland you need to use UL1621 or other integrated/transistor stereo decoder.

robert123 wrote:

Congratulations on your successful construction.It is unbelievable that it has such sensitivity.At my place in podlaskie it would probably be silent.
My radio had to contain these amplification stages,with 5 or 6.It serves me as a bathroom radio.
Did you try to build the HF amplifier as a resonant one - variable capacitor in parallel to L3 and tuning? It seems to me that you would increase its sensitivity even more. Robert R.

Thank you I too was surprised that a design running on just two vintage transistors would play so nicely. This is in part due to the long ferrite antenna, when I put a ferrite rod to the radio it plays even better.
With a resonant circuit on a transformer winding I haven't tried, mainly because I haven't come across such a concept anywhere. This is a specific circuit where even changing the diode turns the whole thing into a generator. However, when I get the chance I will probably try it out of curiosity, as well as using the Schottky diode mentioned by @_ACeK_, SMD I don't have but SB340 does.

tesla97 wrote:

Why are germanium semiconductors really used and not silicon semiconductors?

Because they are historical components and while they are still available you can see how electronics used to be. Germanium transistors actually had a short episode in the development of semiconductors because, around the end of the 1960s, the rapid development of silicon-based semiconductors began.
Some of their properties have an advantage over silicon, e.g. low conduction voltage: the Ueb voltage in a silicon transistor is about 0.7 V, in a germanium transistor it is about 0.2 V, but in general silicon wins in many other, more important respects.

CHOPIN66 wrote:

I'm building a receiver from this book myself, only that this 5 transistor one - with an HF amplifier included in the response and reflex so it should have even more sensitivity.

As I think correctly, you are referring to the schematic from page 368, indeed an interesting design, especially the first stage as the ferrite antenna has three windings.
Plus the final stage on two TG50s and a transformer feeding opposite phase current to their bases. A radio worth building.

PiotrPitucha wrote:

Superheterodyne radio on a single transistor, personally I never liked winding coils that exceeded 10 turns and in today's receivers there are more semiconductors than coils, sometimes none at all.(...)
By the way, I have a question about "cristal" headphones which they passionately use in Japan for such constructions, in very old times the Soviet in-ear version of such headphones cost pennies and now I only find headphones with prices of > 100 PLN

Interesting and unprecedented examples, those from the east have a fantasy when it comes to simplifying electronics. With this heterodyne, I'm afraid there might be quite a problem getting it to solidify and run.
I don't know what the "cristal" are, maybe some kind of piezo? I bought a 2000 ohm model on a sales portal for about 70zl, later on I picked up similar ones on the market but in worse condition for 10zl and a similarly priced Soviet 1600 ohm with potentiometer. With the latter an interesting story, because they are equipped with a plug composed of two joined "bananas" with a raster like a 230 V plug, the seller admitted that he wanted to check them and plugged them into the socket, but as the peasant looked normal and had no crooked ears, I took and discovered that the potentiometer on the cable acted as a fuse
I found footage on yt where you can see and hear such a single-transistor receiver (silicon transistor), it's worth noting what speaker is connected via the 5 kΩ trafo: https://www.youtube.com/watch?v=d6yvyg5N4nc

puchalak wrote:

I remember that the only source of electronics information and schematics available to me at the time, was the library in primary school (youngsters probably won't understand). Most of the few books there were by the same author and even then they seemed quite archaic. Does anyone know what his fate was? Given that the publishers were hooked on the 1950s, he's probably long dead.

For my part, I can say that the author was a practitioner and knew his way around radios I did everything according to the author's instructions and after so many years after publication the radio played practically first time. What his history is I am not able to say, only that he was still publishing in the Young Technician, but in the 1970s from what I could find. There is another author active in radio engineering - Roman Kozak, I don't know maybe they are related?