SG-402, radio from 1940

[Peter08012018]

I'd like to use my TRIO SG-402 as a medium wave source for my reciever of year 1940. I'ts a long time since I have done anything similar. I don't know whether the SG-402 at hand works at all.

1) I would like to listen to the SG-402 to know that it works. My idea is to use a piezo speaker, a diode for demodulation, and a coupling condensator.
2) I would like to modulate the SG-402 from a plain 3,5 mm audio source. Should this work (given I do have a cable from twice Banana to 3,5 mm mono )
3) I'm really lost on how to bring the RF to my receiver. Preferable I would let hang a piece of wire from the output connector near the radio antenna. And ground is just open.
3a) I could connect the SG-402 terminals: Output and Ground, to the receivers terminals: Antenna and ground, directly except with a condensator to eliminate DC.
1a) I do not have a diode at hand, would a transistor from C to E do the job?

Tools I just have multimeters, digital and analog. Is it possible to measure signal output voltage, setting the SG-402 to range "A", as indicated in the manual on page 12? I do have a commercial AM/FM/Tape/CD receiver and a DE1102 receiver, that could receive what SG-402 emits.

Thank you

PS yes I do have the manual in print, probably the best copy in the western world, looking completely unread nevertheless the PDF from the archive would add And I do have the product catalog E-838-C 730820W.

[peter scott]

Hi Peter,

It would be easier to use your commercial receiver rather than attempting to demodulate the Trio output with a diode etc for checking.

That would limit the number of things that you are trying to check at any one time.

Peter

[Peter08012018]

ok, but how do I bring the signal to the receiver? I do not assume that the SG-402 freely emits radiation. (That is I assume it does not radiate even when I connect an unshielded wire?)

[Mark Hennessy]

2) I would like to modulate the SG-402 from a plain 3,5 mm audio source. Should this work (given I do have a cable from twice Banana to 3,5 mm mono )

This will work, but I note that the sensitivity of the SG-401 is 1.5V RMS for 40% modulation.

A lot of devices with a 3.5mm output socket produce an output voltage that is considerably quieter than that. And presumably you'll might want more than 40%, so even a full-size CD player might struggle (they should give 2V RMS with a full-modulated disc).

So it is possible that you might need a pre-amplifier to boost the output signal from the source. Such a preamp should be easy to make (a single op-amp would be my choice, but it could be done with a single transistor if you prefer), or would be available as a simple kit. It could also do the stereo-to-mono conversion in a rather more elegant form that the usual "short L and R"

[peter scott]

ok, but how do I bring the signal to the receiver? I do not assume that the SG-402 freely emits radiation. (That is I assume it does not radiate even when I connect an unshielded wire?)

If the Trio is operational then just having a wire on the output near to your radio's aerial socket should give enough signal for the radio to receive.

Peter

[Peter08012018]

Thank you. I will first demodulate the internal 400Hz with the diode (or a transistor, as I did not find a diode), capacity between. This is within reach today or tomorrow. I do have those solderless breadbords. Thanks for the input-modulation consideration, I will amplify my MP3 player with a transistor to get 2V, or some volts, of audio. That should tell the SG-402 health, given I do not have better tools.

I will also try again, have a wire near the ferrite antenna of the radios, or around the radios at all. First try did not give results.

[Peter08012018]

The SG-402 is healthy, both the internal 400 Hz modulation and the external modulation do work. Although it looks disorderly I post the picture how I have done it. There wasn't better material available. There was no need for amplification, I simply connected the audio out to the external modulation banana jacks. I felt well to hear the MP3 Player in the radio (s).
[attachment=17090]

The VE 40_41 does not work well. I does have a constant humm (loud 50 Hz or 100 Hz signal), no matter what the volume control. The heterodyne oscillator is noticeable, as it disturbes the other radio (DE1102, and another radio) at +455 kHz  approximatively, assuming IF of 455 kHz.

I also do have a Dip meter but don't deeply know how to use it. (Tech Tradiper TE-15 with manual, and works at first sight after soldering the power wires. I am able to notice it on AM/medium wave and FM/88-108MHz receivers at the right frequencies.)

I do have the schematics of the VE 40_41 (and will get them in better quality soon, to edit this post)


{Moderator note: Please do not upload images from Radio Museum here. Instead, provide a link to the relevant page so interested parties can download the images themselves. There are fewer restrictions on using the site these days, so non-members are able to access the files now. The set in question is here: https://www.radiomuseum.org/r/sondyna_vo...40_41.html}

[Peter08012018]

schematic and parts list of receiver Sondyna Volksempfänger VE 40/41, a Swiss receiver from approximately year 1940

{Moderator note: Please do not upload images from Radio Museum here. Instead, provide a link to the relevant page so interested parties can download the images themselves. There are fewer restrictions on using the site these days, so non-members are able to access the files now. The set in question is here: https://www.radiomuseum.org/r/sondyna_vo...40_41.html}

[peter scott]

Hum in your 40/41 could be caused by various things. A common problem is circuitry drawing too much current from the power supply and a possible cause is leaky capacitors.

You could try disconnecting C3,C4,C9,C10,C13 or C20 just to see if the hum disappears.

The smoothing capacitors on the output of the power supply are also possible suspects. C24 and the other one without a number.

Peter

[Peter08012018]

Peter, thank you. It is not really my receiver: I have to sell it or find a new place for it, and shall leave rework and repair to the prospective next owner. I do not have the the professional capability to do it myself and would perhaps spoil the technical and historical value.

I do have some experience  but only at the hobbyist level, and not with the valves generation. I could open the back panel and just tap the components.

Where is the speaker in the schematic, perhaps the coil at the anode of the EBL1?

Is there a way to see that the tuning circuit works? I do have a dip meter, also from the collection-to-be-sold, that should find any oscillating frequency (B in the manual) or resonant frequency (A in the manual). It is Tech Tradiper TE-15, covering 440kHz to 220 MHz, and manual is here

The missing C number might be C25.