Technical, Techniques, Hints, and Tips > Radio Equipment
Old Micron data request...
dodgy geezer:
--- Quote from: HMS Invisible on August 10, 2025, 03:39:16 pm ---The extent of what I hoped to point out is what you seem to already understand.
As well as the half-shot transistors there is an astable timer. A recent thread about restoring a Digifleet transmitter showed one using inverting logic gates.
The ring circuit is completed with a fixed or variable frame, and the output to the rf board will be obvious if you sketch one stage. Without referring to an old Tx or diagram, I think that will be npn collector 4 to 7.
I'll look out an old set & search for the relevant thread about NiCds.
I could further add, which you may have guessed, that the polyester capacitors are the stable timing caps.
--- End quote ---
Alas, I suspect that you think I understand more than I do! I can see that there is a multivibrator feeding pulses into a series of transistors which will switch at variable times depending on the relevant pot setting. But what happens to the signal after that I don't know - I suspect that the electronics I don't understand have something to do with that... But, in the absence of any circuit diagram, does my proposed way ahead sound sensible to you? I suspect that the original circuit worked off 9.6v nominal, and was proposing to use 7.2v NiAmh, since I don't have a bench power supply...
HMS Invisible:
Disregard my earlier description as I was working from memory.
Fig 76 in scimitarjohn's post shows the collector outputs fed into 4001 logic gates but your much simpler circuit will probably use diode logic.
The function is the same as Fig 76. Each one-shot triggers the next one and also triggers the r.f.
In your board it is possibly done via a diode. So r.f. input should be a copper rail with diodes connecting to each channel's transistor collector.
You'll begin to see a similarity with Fig76 where your colour coded polyester caps equate to Ca and C is a cheap ceramic disc cap.
* I just had a closer look at the photo and can see the 4148 diodes.
HMS Invisible:
Here is an RC circuit link you have possibly found. http://sm0vpo.altervista.org/use/rc_enc_02.htm
The 2 and 6 channel diagrams show the 'wired-OR logic' by common-cathode connected diodes. The output is buffered by a BC557 to make a positive pulse.
dodgy geezer:
--- Quote from: HMS Invisible on August 10, 2025, 05:43:36 pm ---Disregard my earlier description as I was working from memory.
Fig 76 in scimitarjohn's post shows the collector outputs fed into 4001 logic gates but your much simpler circuit will probably use diode logic.
The function is the same as Fig 76. Each one-shot triggers the next one and also triggers the r.f.
In your board it is possibly done via a diode. So r.f. input should be a copper rail with diodes connecting to each channel's transistor collector.
You'll begin to see a similarity with Fig76 where your colour coded polyester caps equate to Ca and C is a cheap ceramic disc cap.
* I just had a closer look at the photo and can see the 4148 diodes.
--- End quote ---
I can see the diodes along the output rail - that rail leads into the transistor pair in the mystery electronics. A bit of smplification?
roycv:
Hi, I made up the transmitter and receiver way back. But although 27Mhtz my set is FM not AM. I also have a Futaba 27Mhtz FM Tx but use the Micron rx as it is far more stable and reliable.
Roy
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