Crystal Radio--A Good 1N34A Diode Substitute (4K)
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- Опубліковано 17 тра 2024
- I've gotten a lot of suggestions for alternatives to the 1N34A diode as a detector in crystal radios. I have tested several, including power diodes like the 1N4007 (not worth showing) and the Schottkey diodes (on the oscilloscope it looks good, but is muffled compared to the 1N34A or D9K in actual use).
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1N34A
Forward voltage drop: 1V @ 5mA
Breakdown voltage: 65V @ 1mA
Reverse leakage current: 30µA @ 10V, 500µA @ 50V
Flat Junction capacitance
Lower leakage current
Absolute Maximum Ratings: (TA = +25C unless otherwise specified)
Peak Inverse Voltage, Repetitive (I R = 1mA), PIV 65V
Reverse Voltage DC, V R 20V
Peak Forward Surge Current, Non−Repetitive (t = 1sec), IFSM 0.5A
Peak Forward Surge Current, Repetitive, I FSR 200mA
Average Rectified Output Current, I O 50mA
Operating Junction Temperature, T J +75C
Storage Temperature Range, Tstg −55 to +75C
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D9K
Maximum reverse voltage U(BR) 30 V
Maximum forward current IF 60 mA
Maximum reverse current IR 60 uA
Forward voltage drop at the pn-junction U(F) 1 V
Frequency range, maximum Fd 100 kHz - Наука та технологія
Not sure, but Д9К could be one of soviet germanium small junction diodes of biggest reverse resistance (subtype 'K' of Д9).
The correct diode used to be readily available at every corner "Radio Shack"!
I likely still have a few bags of a dozen diodes purchassed decades ago!
They are worth a lot on ebay!
Something you should try: Anybody can find AA 1.5v cell. Two diodes, one forward biased with 1-10megohm feeding the second diode thru another 1-10meg. Microamps down into nanoamps will allow schottky, Si transistor junctions or whatever - just get close to turn on voltage to keep the impedance high.
Matching the diodes is even better. Germaniums are easiest to match with an ohmmeter forward/reverse. Silicon by Vd. Rectifier efficiency goes way up... with a tiny forward bias. Below turn on; log characteristic changing to linear well above turn on. (simplest RF log convertor used in many RF voltmeter designs).
I saw a circuit diagram with that. Can't remember what it is called.
@@tsbrownie You might want to look up 'temperature compensated' diode bias etc.
Collin's Avionics had 200 service centers worldwide with 200 HP tube front end voltmeters spec'd across thousands of repair documents for hundreds of aircraft.
....only a handful of replacement tubes left from the original batch. And they were desperate! We got a contract to build an RF front end that had to exactly match the curve for AM peak detection. I did it with two schottky MBD701 Motorola diodes in series to get the 700 volts (capacitive divider) and another matched 701 for forward bias. $400k in the back pocket fed 22 employees that month with a weeks worth of tinkering.
edit: Up to 500MHz and small signal, too. There is a ton of radios on commercial airliners - all FCC, FAA approved - no changes to meter specs without millions of dollars in rewrites. AM broadcast band should be quite easy & cheap to optimize...
What about the OA79 ? I seem to remember using this device in a crystal set 60 odd years ago.
"Germanium contact point high-frequency diode, intended for use as detector in FM receivers". There are lots of diodes that sort of work, but give poor sound quality like clipping or low volume. I have not tried this one but it seems made for other purposes.
@@tsbrownie I think it was included in the Philips EE kits, which I had. Worked quite well if I recall.
@@StepDub I'll have to see if I can find one to test.
So does the D9K sound better than the 1n34a?
I cannot hear much of a difference. The D9K might have a higher pitch in the same radio.
Where were you able to find your d9k diode?
I bought them on ebay. (There's a funny song about that from Weird Al Yankovic.)
@@tsbrownie Thank you, sir.
@@adnacraigo6590 I found my order. The shop on ebay is called "Stavr-shop". I don't know him, but he delivered what was advertised. It did take a while.
it is best to check such diodes on a working system
I agree and I did that. For example, the Schottkey diode looks OK on the scope, but sounds muffled in a radio.