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A project log for Clockwork germanium

A retro version of Yet Another (Discrete) Clock, with vintage parts

SHAOSSHAOS 04/04/2016 at 04:0813 Comments

Yann asked me to describe my experiments with germanium transistor here as a project log. So here it is - when I was a kid my family was subscribed to one Russian magazine for kids that once published series of articles about electronic constructor, build from easy available components and in that time (1983) those components were germanium transistors and diodes, so when I noticed this new "germanium" project I immediately remembered those series - this is article that showed how to build NAND circuit first and then RS-trigger from it:

http://zhurnalko.net/=sam/junyj-tehnik-dlja-umelyh-ruk/1983-03--num10
http://zhurnalko.net/=sam/junyj-tehnik-dlja-umelyh-ruk/1983-03--num11

So I took this idea:

and applied to germanium transistor that I have in hands, Russian P-N-P transistor MP25A manufactured in September 1979:

In the beginning I literally replicated the circuit, but added 3 silicon diodes instead of 1 connected to the base (otherwise it did not run):
UPDATE: Article is saying that diodes on the left must be germanium and diode connected to the base of transistor must be silicon - if we do exactly that then it's working, but if you put silicon on the left then base should be connected to more than 1 diode as on schematics above...

I was able to run this circuit up to 10 kHz:

and just for the record - 5 kHz:

Voltage transfer curve looked like this:

Then I added 4th diode:
Then I added resistor 1K from base to emitter and "speed-up" capacitor as described here:
https://hackaday.io/project/6668-aytabtu-discrete-computer/log/23923-more-speeeeed

Final experimental circuit:

was able to run on 100 kHz!

and by reducing voltage to 4V I even got 200 kHz!!!

Now voltage transfer curve looks like this:

P.S. Just ordered germanium diodes to try to be 100% antique ;)

Discussions

Yann Guidon / YGDES wrote 04/07/2016 at 04:29 point

Did you try a Baker/clamp diode across the transistor ?

That might get you some more speed.

I'm also curious of the effect of the resistor values.

There will be "fast" flip-flop latches (with extra parts to speed up at the 32KHz input) and other "slow" gates (Hz) with higher value resistors for lower power...

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SHAOS wrote 04/07/2016 at 06:54 point

I'm waiting for faster germanium transistors MP42A that can do 1.5 MHz (according to datasheet). I will try to make this circuit faster after receiving them...

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Yann Guidon / YGDES wrote 04/07/2016 at 07:09 point

There is no need for > 100KHz with a 32KHz input :-)

The output RC constant also contributes to the slow edges.

Some "fast" computers at the time were using 470 Ohms@6V...

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K.C. Lee wrote 04/04/2016 at 14:09 point

That looks like fun, but you need a lot of germanium diodes because of their lower drops.   Have they invented low drop zener yet?  :)

BTW I saw this circuit back I started electronics. "Sequential Switching Bistable Multivibrator" half way down http://www.electronics-tutorials.ws/waveforms/bistable.html

It uses diodes as switches to steer the clock pulse into the opposite R/S flip flop to make it toggle.

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Yann Guidon / YGDES wrote 04/04/2016 at 14:42 point

It looks fun because it is fun :-) I'm learning a LOT about the history of this technology...

For the Zener, maybe a LED would help but I think @matseng found that it actually slows things down...

Yep, the bistable is a pretty smart design, used by transistorclock.com as well, but I'll also need a more standard "DFF" for the Johnson counters...

Don't hesitate to contribute :-)

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Yann Guidon / YGDES wrote 04/04/2016 at 05:17 point

Block B (at the bottom of the magazine page) looks like a flip-flop, right ?
I'm not sure about the function of all the in/out signals...

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SHAOS wrote 04/04/2016 at 12:01 point

3 and 4 are outputs (Q and /Q), 5 and 6 are inputs (S and R) - capacitors on them probably make them "edge-triggered" kind of thing ;)

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Yann Guidon / YGDES wrote 04/04/2016 at 04:27 point

This log is incredibly awesome :-)

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SHAOS wrote 04/04/2016 at 12:04 point

Thanks, but you can fix my English if you want - I'm learning it only for the last 33 years...

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Yann Guidon / YGDES wrote 04/04/2016 at 12:10 point

Which is a bit longer than me :-)

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SHAOS wrote 04/04/2016 at 12:17 point

Problem is when I started my brain was already pre-wired in Russian ;)

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Yann Guidon / YGDES wrote 04/04/2016 at 15:02 point

And mine in french. But I started early and it was boosted by a pretty weird hobby I had in my childhood... I wanted to make radio transceivers and all the interesting informations were in english...

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SHAOS wrote 04/04/2016 at 17:45 point

I was surrounded by pretty good engineering information in my native language during all my childhood and youth, so I started to read books on electronics in English only after relocating to US in the beginning of this Century. Before that my English usage was limited to help-pages from Borland C++ and then Visual C++ and may be accidental ICQ chatting with Western girls ;)

P.S. 1 hour of English class per week since 3rd grade of Russian school is not counted because it was useless :)

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