Subbu68
Well-Known Member
And another thread on fountain pensI have attempted to draw out my MW Transmitter circuit from memory, I hope I've got it right as the memory is from about 42 years ago
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Sheaffer
JetKing DIY Radio Kits
- Thread starter santaji
- Start date
SheafferOh wow. That's really neat. I feel like building one straight away. I don't think I have an AC125 transistor, but might try substituting it with another PNP germanium one. Thanks for taking the time to draw this.I have attempted to draw out my MW Transmitter circuit from memory, I hope I've got it right as the memory is from about 42 years ago
View attachment 72303
Edit: I may have used a 10k resistor instead of 2.2k in the diagram, with the 0.01uf capacitor coupled with the base of the transistor, I can't seem to remember this accurately.
Subbu68
Well-Known Member
OC76 is perhaps the equivalent.. Saw AC125 on eBay UK.
Perhaps some BC series though Si should fit in with change of resistors? Forgot electronics circuits and how to set the bias, collector current etc.
@reubensm sadly that SONY ICF SW10 did not catch a single station on any band..only a hiss... so a common issue.
Just listened to PM on AIR Ahmedabad at 810kHz on that Sony ICF J40. Crystal clear. Thought it was a local station till they announced the name!!! 1860kms away!!!
And Akashvani Maitree at 594kHz. From Delhi or Kolkata?
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That's a good sign that medium wave propagation is doing well. The Akashvani Maitreyee transmitter is probably in Kolkata. MW can bring nice surprises in the correct atmospheric conditions. I used to be able to hear Japanese stations in India and still have a QSL. I heard Radio Sweden and Langenberg Germany there too, all without an external antenna. In those days I had a two-band Philips Raja DL171 analog radio, which was a very nice receiver.
Post script: The Akashvani Maitreyee transmitter on 594 kHz is in Chinsurah, West Bengal.
Coming back to the topic of DIY radio kits, here is a PCB for making a MW radio from the 80s. It's not a standard board as there is no space for an oscillator coil or tuning capacitor. However, I probably can get around these issues and simulate the Jetking Guru circuit.
Attachments
Subbu68
Well-Known Member
I remember this available in shops.
Elenco I have printed Elenco and Guru circuits..will compare and post later. Elenco audio amp is 4 transistor while Guru has a driver trafo and 3 transistors.
Subbu68
Well-Known Member
The launch news of Maitree said broadcast is from Delhi.
reubensm
Well-Known Member
I recollect these L-Boards, the Osc/Ant coils and bandswitch, were mounted outside the PCB. Little confused about the additional AC127 (towards the bottom of the board, near the 0.01uf cap). That looks like an interesting addition to the circuit. The rest looks pretty much standard. Could not seem to locate the OC79 as well
Subbu68
Well-Known Member
I too wondered why that AC 127 when everything else is silicon (except amplifier section front end) and similar topology as Guru. Yes the detector diode OA79 is missing. Just compared the board with the circuit. The values are different but components seem to match Guru. If you got the parts though the Germanium transistors and driver transformer maybe a pain to get, you can build a Guru. Or up to the detector stage and hook it up to an amp.I recollect these L-Boards, the Osc/Ant coils and bandswitch, were mounted outside the PCB. Little confused about the additional AC127 (towards the bottom of the board, near the 0.01uf cap). That looks like an interesting addition to the circuit. The rest looks pretty much standard. Could not seem to locate the OC79 as well
This board can be used for any number of AM bands I think.
I saw one circuit where they used B-E shorted Ge transistor in place of OA79.
And this link validates it https://nandustips.blogspot.com/2014/05/alternative-detector-for-shunt-fed.html
reubensm
Well-Known Member
sometime ago, when i enquired at local stores, they said that these new versions of AC188 can be used as a substitute for AC128 on these radio boards and no heatsink is needed. I havent tried it though.
regarding the short transistor in place of OA79, that is something unique, first time I have come across this idea.
regarding the short transistor in place of OA79, that is something unique, first time I have come across this idea.
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Subbu68
Well-Known Member
I think my Jetking Skylab 2 band had them in the output stage. Or was it in the one my bro made I don't remember
I have some plastic encased transistors labelled as AC128. However, I suspect that they are actually renumbered PNP silicon transistors with properties very similar to other silicon transistors like 2N3906, which I also have. I do not expect them to handle as much power or sound as good as proper germanium AC128s or AC188s. Since I also had some germanium AC128s in my parts box, I used those with a 4.5V driver transformer similar to the Jetking Guru one and obtained acceptable results. I used a standalone board and an 8 ohm speaker to test the circuit. I used a proper heatsink too.
I actually found one in my grandparents home had to clean it is working it needs some tuning to do
Do u still have the manual
Subbu68
Well-Known Member
Tuning is no big deal if it is working.
I just did my daughter's kit (Elenco AM) from my memory.
are you looking for the manual to tune it?
reubensm
Well-Known Member
nice kit build
I think I am late to the party, after all efforts I could find one from local Pune online seller.
See if this could help you -
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