Making Point Contact Transistors

[Jeri Ellsworth] is back at it again. We seem to cover her work a lot here. Her latest video above covers how she created a point contact transistor from a 1N34 germanium cat whisker diode. After opening the glass casing on the diode, she uses sharpened phosphor bronze metal from common electrical connectors as the collector and emitter. A 330 microfarad capacitor charged to 20 volts and then discharged though a 680 ohm resistor to the base and collector leads forms the collector region. Her test jig is a simple oscillator circuit such that a properly formed transistor will start the circuit oscillating and make and audible sound. We look forward to more esoteric knowledge of electronic devices being brought to our attention.


  1. biozz says:

    these are like the first type of transistors made right?

  2. zerth says:


    Yes, the first commercial transistors were made of germanium at AT&T, silicon coming several years later from Texas Instruments.

  3. grenadier says:

    I’ve done this before and have made an audio amp from one. I’ll have to try this again.

  4. p knight says:

    The queen of nerds. I could sit down with this woman and pick her brains for years. Hot and intelligent. Its like looking in the mirror.

  5. therian says:

    Unbelievable. It took many moths for Japanese to find under microscope right contacting spot on crystal when they try to back-engineer American invention.

  6. Oren Beck says:

    Before we had transistors, we had “cat’s whisker” radio diodes. And the commonplace effect of having to probe for a “Hot Spot” on whatever chunk of Galena-or a rusty razor blade, that was being used in your radio.

    It was explained to me that the serendipity of static charges on longwire antennas frequently making a spark discharge-created an induced “hot spot” of sorts. Which, to forgive the pun, sparked research into replicating the effect. And some of what was discovered, seems to have become either “trade secrets” or just written off as too unstable for production uses.

    I was told that’s why sloppy process control in some lead bonding methods/spot welding variants can produce rectification effects. With the aforementioned unstable=difficult to produce reliably results.

    The use of Capacitor Discharge to form a contact zone is a good step towards reproducible hobby built semiconductors,

  7. George Johnson says:

    This girl is gonna go far, and I’m really glad to see it to. Just about every other young girl should be looking up to her as a model. No reason they can’t do this too.

  8. Whatnot says:

    She has a way of speaking that sort of makes things seem mysterious, but without the usual laying-it-on that they use for ads for movies and such.
    I think she might be a person to hire for a mystery/scary movie, or ad for such a movie, she has a bit of the effect that worked so well in ‘signs’.

  9. Ugly American says:

    These videos would be great for science & electronics teachers.

    A workshop for teachers would be cool too.

  10. kristian says:

    i move for a new category of hacks in the rarely-used tag list to the right called jeri-hacks (jeri-rigs?). all in favor?

  11. biozz says:


    wow thanks

    i have baught tons of diffrent types of transistors in my day from FETs to MOSFETs to BjFETs but never heard of a PCT before XD

  12. strider_mt2k says:

    I haven’t seen her videos before, but I’m really impressed with the explanations and techniques!

    Totally makes me want to try this!

    Folks like this are what make this hobby really great.

  13. bob says:

    go back to the second world war and the POW…..

    a lump of coal/coke (as in carbonised form not the white powder) can be used as a diode

  14. blue carbuncle says:

    Not for me.

  15. zeropointmodule says:

    wonder if this approach would work for SiC crystals?

    i seem to recall reading somewhere that SiC tunnel diodes are made by adding a small piece of silicon onto the SiC, heating it to 1000C and rapidly cooling to form the molecular thickness tunnel region.

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