Foxhole Distortion? (DIY razor blade diode clipping)

[EBK]

And, if you are interested, and can follow it, here is my layout:

[iainpunk]

hey, i think i get it, just an mxr dist+ wit a pot in between the diodes and op amps.
i'm not really in to the whole stripboard/vero thing, i chose the pad per hole side in "the war of the prototype boards".

i also think there is a good middle ground, which still gives you the possibility to make the circuits compact, but also has the ease of use of vero (ignore the arrow)

[Gus]

Have you seen this page?

http://www.sparkbangbuzz.com/

http://sparkbangbuzz.com/zinc-oxide-diode/zinc-oxide-diode.htm

[EBK]

Have you seen this page?

http://www.sparkbangbuzz.com/

http://sparkbangbuzz.com/zinc-oxide-diode/zinc-oxide-diode.htm

Interesting. Thanks for sharing!  I have to melt some pennies now to try this zinc blob diode.

[j_flanders]

Or these:
http://halestrom.net/darksleep/blog/011_copper_diodes/
https://hackaday.com/2016/05/01/home-made-diodes-from-copper-oxide/
https://www.instructables.com/id/How-to-make-a-copper-oxide-diode/

I have many other links but they're on another computer. (includes the ones Gus posted)

Last year I spent countless hours trying to replicate some of the experiments to use them in a distortion pedal.
But I had a real hard time getting them to work. Really frustrating.
At one point I found myself oxidizing and 'blueing' every kind and piece of metal I could find around the house.
Eventually the wife gave me 'that' look. Made me feel like a 10 year old. 

Some kinda seemed to work but were still behaving weird:
-it clipped in both directions, I did not need two diodes. 
-it needed quite a bit of current and even a just little too much current destroyed the diode or 'contact point'.

[EBK]

This evening, I did some quick tests to see if my DCA55 would believe I had a diode.  Depending on the spot the pencil touched, I got one of three results on the screen:
1) No device
2) Unknown/faulty device
3) Depletion mode P-channel MOSFET (source and drain terminals)


I'm guessing that third result, if any, is probably indicative of the diode operation.  I would've guessed it would report it as a Schottky diode though....

[EBK]

No clipping yet.



Not giving up.

[duck_arse]

have you tried the blade edge as yet? not for shaving. obvs, but for diode-ing. [perhaps stand the blades cutting edge up, w/ pencils wrinting points down.]

[amptramp]

Here's a classic galena detector with variable arm position to find the best point:



This used to be a standard for crystal radios.  As well as these, Philmore used to make crystal radios with the cat's whisker contact already placed in the best position and sealed under a glass dome:



This gives you a better view of the dome:

[EBK]

I've started experimenting with a new probe made out of an old acoustic guitar string (phosphor bronze).  The winding is the whisker, and the stiff core provides an adjustable spring.

Again, no idea if what I am doing makes sense.

I think I need to clean and retorch the blade.  There is a lot of pencil graphite on it from moving the pencil probe about a thousand times.

[TheOtherMrBill]

I'm glad I found this thread because I'm looking into making this very thing. It was looking for real measurement data that brought me here to this thread. The fact that Erik EBK put the picture of the o-scope was exactly what I was looking for. Thanks for that. But, I can assume that since it's 4 or 5 years later that this never really got working. I think I understand why.

The blue steel carbon pencil detector from a foxhole radio is a point-contact diode. Looking for the characteristics of that pointed me to an electrical engineering site that compared point-contact diode to PN junction and Schottky diodes https://www.eeeguide.com/what-is-schottky-diode/. There's a graph towards the end that shows the behavior. It's not like it reaches a threshold forward voltage and then current flows, it's much more gradual. In fact, it resembles a much more gradual parabolic curve

I = (C2*V + C1)*V + C0

If I had experimental measurements for the forward voltage (V) and current (I), I could compute coefficients for it.

Anyway, it's not going to hard clip the way "normal" diodes do with a forward voltage. In reverse... maybe, but then you would have to set a bias voltage on the opposite side for the signal to push through. Curious to see if anything came out this project in the past few years.

Bill