Busch AM radio with High Impedance HF amplifier

[Frankje]

Hi all !
To celebrate the AM radio area, I would like to make acontribuition around the Busch system
The first RF amplifier stage consists of a fet bf245 which does not load the antenna circuit due to it"s high input impedance.
The FET has a RF coil in the Source circuit.
The signal from the Source is connected to the radio ic ZN414 which takes care of further amplification and dedection.
The LF stage is a LM386 ic which drives the speaker.
Amazing how sharp stations can be tuned with good separation.
If anyone is intested to rebuild this circuit, let me know and I will provide the building details.
Greetings

[pingi66]

Hi Frankje,

first I have to say that you have done a real good job. Unfortunately I have no experience in Busch system, but I am very interested in all kind of AM-receivers. And of course I'd like to perceive your offer to provide some building details especially the first RF stage.

You can contact me on my private account.

Kind regards
Sven

[Frankje]

Hi all,
Since the publishing of this circuit, I didn’t find some time to draw the schematic, so here it is.

I’ve been using this radio on my hobby desk for quite a while and since it performs very well, I thought it would be a good idea to use this circuit in the EE Philips radio engineer.
Can someone rebuild this circuit, either on a BUSCH or a Philips platform to compare the results ?
I also made a little video, I will publish this later.

Greetings

781FCDAA-0E9B-44D5-A6FE-A18368A1B799.jpeg (868.46 KiB) 5797 mal betrachtet

781FCDAA-0E9B-44D5-A6FE-A18368A1B799.jpeg (868.46 KiB) 5797 mal betrachtet

0D9BC2AC-A300-4E46-A7C0-7D5776B5B21D.jpeg (606.68 KiB) 5797 mal betrachtet

0D9BC2AC-A300-4E46-A7C0-7D5776B5B21D.jpeg (606.68 KiB) 5797 mal betrachtet

[pingi66]

Hi Frankje,

thanks a lot for the schematic, it's really a nice circuit.

But I think that there is something missing, there is no power supply for the TA7343.

Kind regards
Sven

[Frankje]

Hello Sven,
You’re completely right !
So, I post here the corrected schematic.
Greetings

1070B6B9-6AFD-4717-B8F7-F6C53C07B8D1.jpeg (570.41 KiB) 5746 mal betrachtet

1070B6B9-6AFD-4717-B8F7-F6C53C07B8D1.jpeg (570.41 KiB) 5746 mal betrachtet

[Masteraah]

Hi Frank,
I built your circuit, but I only get very low static, almost not hearable... is that normal?
Your schematic uses a 10k Poti, which I don't have, I used a 50K... can that make a difference?

Regarding LM386: I used pin 5 as output and pin 3 as second input... is that correct?

And just for curiosity: Why did you not used the AM IC from the original 2070 kit but TA 7642? Is that a better version?

Thanks for your comments,
Andreas

[Frankje]

Hi Andreas,

Well, this circuit dates from already 3 years ago. Maybe many stations have gone in the meantime.
I will rebuild it one of these days and have a listen to what we still can receive !
I remember that I could easily tune in to many British, Polish, Italian and Spanish stations with clear reception, mostly in the evening with a clear sky.
In daytime, there was no good reception at all !
Try it once in the evening !

The TA7642 is the same as the ZN414, found in the Busch studio 2070 sets.
Indeed, pin 3 is the input and pin 5 is the output of the LM386.

Many greetings,
Frank

Nun, diese Strecke stammt aus der Zeit vor 3 Jahren. Vielleicht sind inzwischen viele Stationen weg.
Ich werde es eines Tages wieder aufbauen und hören, was wir noch erhalten können!
Ich erinnere mich, dass ich leicht viele britische, polnische, italienische und spanische Sender mit klarem Empfang einstellen konnte, meistens abends mit klarem Himmel.
Tagsüber gab es überhaupt keinen guten Empfang!
Probieren Sie es einmal am Abend!

Der TA7642 ist der gleiche wie der ZN414, der in den Busch Studio 2070-Sets zu finden ist.
In der Tat ist Pin 3 der Eingang und Pin 5 der Ausgang des LM386.

Viele Grüße,
Frank

[Masteraah]

As a comparisson I built the circuit from page 22 of the 2072 Busch set:

AM4.jpg (182.35 KiB) 2054 mal betrachtet

AM4.jpg (182.35 KiB) 2054 mal betrachtet

AM3.jpg (501.29 KiB) 2054 mal betrachtet

AM3.jpg (501.29 KiB) 2054 mal betrachtet

However, I did not reiceive anything, just noise... It seems that it needs a real good receiver and antenna to get something as most AM stations disappeared...