Clockwork germanium

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

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Imagine you're in the ealy 20th century, with the old technology but with all the knowledge of today. What would you do ?

* Resistors and capacitors are well known and industrially manufactured
* Piezo-electricity was studied by Pierre & Jacques Curie in 1880. In the 1920s, Pierce nailed oscillators and in 1927, the first quartz-synched clock was built by Warren Marrison and J.W. Horton at Bell Labs.
* Point-contact diodes are from the 1900s too
* The LED effect was first observed in a point-contact diode in 1907. Actual production began in the 1960s.
* The bipolar transistor was discovered in 1947 (more or less simultaneously at Bell Labs and in France by Germans)

Let's say we're in the 1950s and gotten seed funding. Making a clock would be a logical application despite the higher parts cost compared to radios. Logic gates are more tolerant to leakage, low gain and fab variations. Indeed, early computers were built out of low-grade transistors!

This is the "neovintage" version of #Yet Another (Discrete) Clock using original old parts as much as possible "for research purpose".

I (@Yann Guidon / YGDES) receive help from two contributors who have more experience with Germanium than me: @Alexander Shabarshin and @jaromir.sukuba. This is invaluable to decypher russian parts and cyrillic data sheets or circuits, thank you guys ! Alexander writes about one half of the logs, and he also started his own germanium clock project using circuits we develop here.

Expect power consumption to be higher than the MOSFET version, but fortunately, the invention of the transfer resistor is saving us the insane amounts needed to power the heating elements of vacuum tubes. Relays don't need high voltages either ;-)

Some design constraints

  • old/vintage parts wherever possible and whenever available
  • 4.5V power supply from alkaline batteries (so power consumption should be kept low and supply varies between 4V and 5V))
  • PNP Germanium transistors (unless NPN is really required but apparently not)
  • Low frequency Crystal oscillator as discrete clock source


The clock is made of a similar design as the #Yet Another (Discrete) Clock but the technology is a bit different so one single module will not fit all. We mostly need

  • Divide-by-two cell for the frequency divider (similar to )
  • Flip-flop cell for the Johnson counters (2, 3 and 5 stages). No schematic defined/found yet but it might be adapted from the 4-T of this 50 years old circuit:

The Johnson counters directly drive the LEDs:

This diagram must be corrected because it works well for MOSFETs but Ge BJTs behave differently, the previous sentence means "there is no 7-segments decoder".


The chosen clock source is a 18KHz quartz resonator in a glass tube. Total: 39 FlipFlops.


1. 1st approach
2. Testing Germanium transistors
3. Crystal oscillator
4. Germanium diodes
5. 2nd approach
6. Testing Germanium transistors (2nd part)
7. Crystal Oscillator (Germanium Edition)
8. Triggering Germanium
9. Vintage transistor book
10. Got Quartz !
11. Reverse-engineering vintage quartz resonators
12. It just works
13. More ingredients to cook germanium
14. PCB received
15. New inventory
16. Easier frequency division
17. Another interesting BJT DFF circuit
18. More bistables
19. Even more bistables !
20. Even more bistables: plot twist !


  • 400 × OC70 Vintage Germanium PNP transistor

  • Even more bistables: plot twist !

    Yann Guidon / YGDES10/17/2017 at 12:10 2 comments

    Today I received an email that I couldn't expect at all. Enjoy !

    I enjoyed your hackaday posting of the 2n554 flip-flop circuit.  I built the computer described in that  Popular Electronics article in high-school in 1964.  Those circuits were later reused in my KB/67 (Kalin-Burkhart) project.
    Here's a bit more about the history of that flip-flop circuit. I was always curious where that circuit design originated, and did some follow-up.  That flip-flop was also featured in the January 1960 issue (page 65) of Electronics Illustrated in an article by Ronald Benrey.  He contributed many projects to electronics magazines during that time.  His homemade satellite appeared in the October 1958 issue of Popular Electronics.

    Looks like the flip-flop circuit is from Performance Tested Transistor Circuits, (page 47) published by Sylvania in 1958.  Although that circuit uses a different transistor, 2n307, Benrey substituted the 2n554,  which was a common substitution.

    Before finding the Sylvania document, I thought perhaps that the circuit may have come from a Motorola publication.There was a 2n554 application bulletin published, which I've not been able to find.  But I did find an ad (attached) for that bulletin.  At least from that write-up, the flip-flop circuit is not included.

    (7% distorsion, yay !)

    That demo computer described in the PE article also made the cover of Computers and Automation in Nov 1960.
    Very brief description on page 20. One of these units was listed on ebay last year, 2 photos attached.

    How awesome is that ?

  • Even more bistables !

    Yann Guidon / YGDES02/04/2017 at 22:40 16 comments

    The last log (More bistables) found some explanations of the weird flip-flop schematic I initially found.

    Today, a comment by RSMilward on brought a new light to the mystery !

    This one comes from an even earlier publication (1961) in Popular Electronics, hosted on :

    From the experience with the 10TFF and looking at vintage circuits, I realise something about edge-triggered flip-flops with only 2 transistors. In the 10TFF, a temporary value is held as a charge on one transistor's gate. This principle is found in the 2BJT circuits with actual capacitors, which are "protected" from the previous stage by a series resistors.

    This resistor is critical for the speed and power consumption. The RC constant must be adapted to the system's speed. That's where the 2BJT circuits reach their limit... For the "slow" parts of the clock, this is not a problem and this will save quite a lot of germanium parts, but there are quite a few diodes and other passive parts.

  • More bistables

    Yann Guidon / YGDES01/18/2017 at 23:46 0 comments

    I still feel that the divide-by-two diagram in the "details" page is messy.

    I tried to address this (rather critical) issue in Easier frequency division but the principle is not reliable enough.

    I just stumbled on a better laid out circuit at

    The old (1968?) book also explains how the whole thing works.

    I faintly remember seeing this sort of circuit in one of @Shaos's russian books but 1) I don't read russian 2) the circuit was pretty messy too...

    I'm concerned that the OC70 might not be fast enough to work at 18KHz so I must find a more reliable (ECL-based ?) method for the first stages of the predivider.

    I'm puzzled by the circuits of that time : they use 3 power rails (-Vcc, 0V and +Vcc). +Vcc seems to be used only as a "pull-up", maybe to accelerate charge dissipation and recover from saturation. I'll have to substitute with Germanium diodes for Baker clamps...

    Now, considering that a ECL latch uses about 7 transistors (a DFF uses 14), the predivider would be too expensive with this approach. However, the circuits close to the resonator will work close to the maximum speed of the transistors...

  • Another interesting BJT DFF circuit

    Yann Guidon / YGDES01/09/2017 at 03:25 17 comments

    I've been pretty confused by the 2-transistors latch that is shown on the project details page. I've been looking of a simpler, yet compact DFF circuit that uses few transistors.

    Today I've done some research on the subject of #CBJT Logic and I came across this PDF :

    "Figure 5 shows the realization of a triggered bistable circuit with complementary transistors. The set-reset function is here performed by a symmetrical transistor;

    if A is 0 volts (true value, "1"), the symmetrical transistor will work as an emitter follower and, by a pulse at its base, set the bistable circuit;

    if A is not 0 volts (false value, "0"), the transistor will work as a collector follower and, by a pulse at its base, reset the circuit."

    The latching cell contains a OC47 and OC141.

    OC141 is NPN germanium, OC47 is PNP (like the OC70 I have).

    I am confused by the transistor symbols but I can try to reverse-engineer the circuit...

    The right side is the latching part so the base loops to the collector of the other... How do I interpret the OC141 with 4 pins ? Well the right and left are probably the same node...

    Creating a latch cell is pretty easy and does not depend on the polarity of the transistor so that's not critical.

    What I'm after is a way to change/force the value with the least parts possible and the OC141 on the left does just that. This is the most interesting part !

    Let's notice the two capacitors (of identical values: 4.7nF) and the resistor divider (10K, 10K) on the A input.

    The capacitor on A stores the data's charge, while the series input resistor isolates it from the source circuit (probably to reduce data leakage while it changes from a simultaneous clock pulse).

    The base is clearly (from the text) connected to the resistor divider 22K/2K, energised by the clock signal, through the series capacitor.

    The point is clearly how they use a NPN to work as a "pass gate", while the input value is held in the capacitor. The clock capacitor has a similar value so both discharges are simultaneous.

    Now, the awaken @esot.eric will notice that when A is low, B is high and a rising pulse appears on T, then the pass transistor is ... reverse biased ? Current will flow from B to the input capacitor (but not A because of the resistor).

    Does that remind any Eric of a "almost functioning" circuit with a mistaken transistor ?

    Whatever the case, it's very interesting because each DFF uses only 3 transistors, no diode (though I'll add one for the reset), and the circuit can be tuned for other voltage rails. It shouldn't be hard to modify it for an all-OC70 design.

    With "only" 3 transistors, plus 2 to drive the outputs, the whole clock system requires something like 39DFF×5=195 transistors. Add some more for housekeeping (oscillator, buffers, drivers, decoders...) and this might reach 250 transistors, which is a desired outcome. The "pass trick" exposed above might be the detail that makes this whole project realistic.

  • Easier frequency division

    Yann Guidon / YGDES05/23/2016 at 04:10 0 comments

    The OC70 is a "lazy" transistor and the 8KHz oscillator is close to its maximum working frequency. Yet this frequency must be divided because the digital counters need "time" to work. I've been naturally thinking of an analog circuit that oscillates at 1/2 or 1/3 of the input frequency, and gets synchronised to the input frequency, which would be the reverse of an "overtone" frequency multiplier.

    Well this idea has been studied for a century already, as mentioned in


    This procedure was reversed by Hull and Clapp72, who discovered that the fundamental frequency could be controlled by coupling the high-frequency source directly into the circuit of the multivibrator. This, in fact, is a general property of any oscillator in which the operating cycle involves a non-linear current-voltage characteristic, being most pronounced in those of the relaxation type. Van der Pol and Van der Mark in 1927 reported on some experiments on "frequency demultiplication" using gas tube relaxation oscillators73. The multivibrator is, in effect, a relatively stable relaxation oscillator74, and with slight modification has been used extensively as the frequency-reducing element in quartz-controlled time and frequency standards throughout the world.

    One serious difficulty with the multivibrator type of submultiple generator has been that, if the input fails or falls below a critical level, it will continue to deliver an output which, of course, will not hen have the expected frequency. Certain variables in the circuit, such as tube aging, may cause a similar result. With this in view, a general method for frequency conversion has been developed by R. L. Miller75, in which the existence of an output depends directly on the presence of the control input. The basic, idea involved in this, now known as regenerative modulation, was anticipated by J. W. Horton in 191976 but had not been developed prior to Miller's investigations. The circuit of a regenerative modulator in its simplest form as a frequency divider of ratio "two" is shown in Fig. 12.

    Fig. 12--Frequency divider for ratio TWO employing regenerative modulation.


    So once again, reinventing the clock with old parts lets me discover century-old methods. I have seen a few relaxation oscillators used as frequency dividers and they look more practical than flip-flops, can run faster and use less parts.

    It is possible to do a relaxation oscillator by combining a PNP and NPN transistor to create a SCR such as the "SUS" 2N4989:

    So it was a very fortunate idea that I got some OC139 (NPN Ge) !

    For the Zener, a LED will also work, I suppose ;-)

    The other benefit of a relaxation oscillator is the possible cross-coupling with the Xtal oscillator to "help" or "kick" it into oscillation.

    My initial idea was more using an astable multivibrator. In fact that's what Injection-Locked Frequency Dividers (ILFD, discovered at Crystal oscillator with MOSFETs (new episode)) do, by modulating the operating voltage of the multivibrator with another transistor. The advantage of a multivibrator is that it uses only one kind of transistors so it will not use my short supply of 0C139.

  • New inventory

    Yann Guidon / YGDES05/22/2016 at 19:46 0 comments

    As time progresses, I (Yann) am turning more toward European sources of vintage transistors. Honestly, I bought the first Germanium transistors (the soviet МП13Б and МП26А) as "double diodes" for the reset signals and only later I thought about using them for switching purposes.

    Still, they look like transistors and the performance is not fabulous. I can get away with many quirks but the efforts must be worth it. I want the parts to be and look special, what's the point otherwise ?

    So far I think I have enough transistors to start maybe one or two full-scale assemblies, using:

    • AF137 and G106T (Telefunken, PNP, 25V, 60mW, β around 60, 35MHz, to be confirmed) as well as AF200 (another 4-pinner)
    • AC125V (package similar as above, β>90, 30V, but only 1.7MHz)
    • OC70 (black glass, unmarked)

    The Telefunken parts look great to design a "numbers processing circuit". I'm not sure what can be done with only 400pc though.

    The AC125 are not fast enough for high speed processing but can manage the clock oscillator and prescaler of the clock. Or more. It's germanium-y and can make a nice clock too. The datasheet is pretty complete (if it's really from the same manufacturer).

    But the OC70 is the thing for this Germanium Clock project, with its totally odd look and antique characteristics, a blast from the late 50s !

    Transition frequency of 15KHz ? Wow that's not fast... So it can only be used for the counter of hundredths of seconds, not closer to the prescaler. I have read somewhere that Mullard's OC70 were used in the first British transistorised computers and digital devices so "it should be ok" and it should suitable for the clock's slow counters.

    But the look is just right. If you don't know what it is, you are only left with conjectures:

    And this is one of my goals for this clock project : it's really a clock but you have to think beyond your habits :-) It's always good to relearn old things...

    Now that I have the parts, I can start the design of the elementary blocks : latch and counters. There are about 40 blocks but I don't know how many transistors will be needed. I don't even know who manufactured these or when. I'll have to test them !

    Update: A pair of randomly picked OC70 of this batch can run the Xtal oscillator at 8KHz !

    I can better appreciate their characteristics : they are "lazy" with just enough gain but low bandwidth. They can be "boosted" by increasing the power supply voltage though. Oscillation can be sustained at 3V but needs double to startup. The dual-stage amplifier circuit works great and it's important to match the sensor's trimmer to the quartz impedance (the trimmer is set at 16.45K). The other pot is used to center the signal/oscillation in the working range (check with the scope if there is no saturation) and you're done.

    What is now missing is:

    • Fine frequency tuning (I must have #Hacking a FE-5680B rubidium reference clock working again...)
    • sufficiently fast logic for the prescaler (darlington ? non-saturating logic ? higher voltage ? germanium Baker clamp ? sorted gains ?)

    BTW, the quartz emits a faint audible whine at 8KHz even when driven with a nice sinewave. Now I understand why 32KHz was chosen, after the first clocks at 8KHz, it was not just a matter of size. Energy gets dissipated through the vibrations and it's proportional to the size. OTOH the very low frequency quartz are large and have a high inertia, which is hard to get moving first, but better stabilises the operation. Conclusion: lowering the amplitude reduces the losses...

  • PCB received

    SHAOS04/19/2016 at 01:20 3 comments

    I've just received 3 PCB of "Germanium NAND" from

    It was drawn in gEDA "pcb" software (images generated by OSHPark service):

    and represents this schematics:

    Also I got 3rd (1958) and 4th (1959) editions of "Transistor Manual" from General Electric Company with more schematics of computer components utilizing germanium transistors:

  • More ingredients to cook germanium

    SHAOS04/17/2016 at 01:22 3 comments

    More retro stuff received:

    And in the quartz it looks like only 3 wires are there out of 7 (some of them were connected together or not connected at all):

    It's 2 contacts connected together for 1 side of the crystal and 2 separate contacts on other side of the crystal, so I cut all other wires to keep only 3 important ones...

  • It just works

    Yann Guidon / YGDES04/16/2016 at 01:43 11 comments

    In the previous episode, Reverse-engineering vintage quartz resonators, we had a lot of questions and a few hints. The best way to be sure was to try them.

    I took the previous board (see Crystal Oscillator (Germanium Edition)) and removed the 32768Hz Xtal. Instead I put a 3-pins socket, with ground in the middle. I put the 2 crystals (in succession) on a connector and tested them.

    The wristwatch crystal needs quite specific parameters to work correctly.

    The russian crystal just worked, oscillating immediately with the parameter of the tiny crystal. Oscillation persists even with both trimmers cranked up to the max (47K Ohms) at 1.5V (though startup was slow). But even then, it just worked, using low gain transistors (hFE=37).

    I feared that operating it would be difficult, like requiring more driving energy because of the larger size (higher motional inertia) and other factors. But the tube just "rings". No I can't hear it but it picked up the oscillations much better than the tiny tuning fork, requiring less energy.

    I suppose that the lower frequency also contributes to this sensitivity, since the transistors are not ultra-high performance. So the rough MP13B might work as well. A recent planar transistor will fly. I should still investigate the MOSFETs...

    One surprising result was that it works better when the "large electrode" is on the driving side, leaving the small electrode to the sensing side. I haven't tried all the 6 combinations/permutations of the pins yet, though, but this would be a very interesting experminent. But first I need a tool/measure to measure the gain, other than the time taken by the oscillations to reach full range.

    Whatever the result, my bet on this tube has been a clear win, on every account. It costs more than a dumb wristwatch crystal but it requires less driving energy so it's energy-saving. It looks much better, might have a better temperature stability and it's pretty unique...

    We'll see soon how it behaves and how it is tuned.

    By popular demand, here is the updated schematic :

    R2 and R4 have been increased because the signal saturates fast, and saturation is not good. Actually, the best is to have a small sine, less distorsion and better accuracy.

    Due to the higher sensitivity of the crystal, R1 and R3 can be increased as well.

    C2 must be evaluated. I don't have the means to calibrate this frequency yet (my #ScoPower gizmo is fixed to 32768Hz). I'm waiting for my Rb source and a DDS.

    I will have to evaluate the effect of leakage, thus of temperature-induced drift.

    To compensate power supply voltage drift, I'll probably add a micropower voltage regulator. No Zener diode because of the tempco and the worse regulation ratio. This is why I try to make it work at a lower voltage than the rest.

  • Reverse-engineering vintage quartz resonators

    Yann Guidon / YGDES04/15/2016 at 16:43 0 comments

    The seller provided the following picture but even after receiving the crystals in tubes, many questions remain.

    First, is it series or parallel resonance ?

    Then what type of cut is it ? has many choices but many are vague. I can already filter with the frequency range (when provided). The shape of the crystal cut and the plating/electrodes reduce the possibilities further : the oscillation mode is obviously "bending", like a vibraphone bar. From

    The 4 connections are at the "immobile" points of the crystal, to prevent damping, at 1/4 and 3/4 of the length of the crystal (though it looks like 1/6 and 5/6 to me in my tube).

    The possible cuts are

    The electrodes prevent most harmonic/overtone vibration modes because the "middle" electrode (2/3) short-circuits opposite charges. So the frequency and waveform/shape would be quite pure and stable.

    The "passport" that @[skaarj] translated (in the comments) mentions -80°C to +80°C operating conditions, which are another hint for the cut. It seems to be symmetric around 0°C, which is unusual. Finding (or measuring???) the temperature response curve would help even more. Does anyone have a climate testing chamber ?

    Initially I feared that the frequency stability would be poor but it might be the reverse, this will have to be measured and I suppose that the germanium leakage will be the greatest source of variations. I'll probably have to find/imagine a balanced/symmetrical oscillator circuit using matched pairs...

    One more hint would be the internal connexions. Some electrodes are connected to structural elements, hence have higher capacitance. Some output wires are connected in parallel with the structure, as well. contains a very interesting hint at fig.8 :

    (Wait: what is this "bridge-stabilised oscillator" ? I have to look that up
    Update: ok, no, it works in series resistance resonance but I don't know if the tubes are rated for series or parallel mode)

    The two bottom circuits use the classical 2-electrodes quartz but the top one has 4 electrodes, more like my tube !

    I suppose this 4-electrodes crystal works in a different cut/mode but from there, my latest guesses are confirmed and I suppose the following:

    • short electrode (1/3) for driving the crystal (with enough drive, but smaller surface if compensated by high gain circuits)
    • long electrode (2/3) for collecting the charges and providing feedback
    • opposite side electrode (full length, 3/3) is grounded (otherwise, relative to what point do we measure the charges ?)

    Or maybe swap 2/3 and 3/3. I'll have to test that... After all there are only 6 combinations :-D


    • The quartz bar is 30mm long
    • contacts are at 7.5mm from each end
    • The short electrode is 8.3mm long

    Things add up nicely :-) 7.5×4=30mm, so the oscillation is in bending mode, perpendicular to the electrode platings. Contacts are placed at the point of least motion, to prevent attenuation, at 1/4 and 3/4.

    The puzzling part is the 8.3mm of the short electrode, I don't know why this length. The ±3.6 ratio does not correspond to an obvious mathematical relation. It's close to 3.3 and has misled me but maybe the measurement is not precise enough.

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Enjoy this project?



add_ocean wrote 09/26/2017 at 21:52 point

Well, let me add some ideas :)

While i studied "yet another discrete clock" project (very neat D-type flip-flops and Johnson counters), i must admit that binary logic is best in that it is very reliable and tolerates components drift but at cost of complexity.

Is actually binary a must? Why not to have "analog" appliance, at least it will be an unusual approach.

This is schematic of divider (from book described supposedly tested designs of amateur builders):

There are oscillator and two stages of divide by 10. It says that each stage can divide by max 7 with ferrite cores, and by max 13 with now obsolete Al-Si-Fe cores (huge 36 mm diameter, low mu, low frequency, high flux. I believe modern iron powder might go just as fine). First coil is 0,33 Henry and next 3,3 Henry. Of course main disadvantages are complicated adjusting tank freq. and need for thermal stability of LC tanks (i believe 2,5% or better in whole temperature range ). Pobably need for careful  temp compensation?

Then, simple ring counter that drives LEDs, no binary D flip flops. More ring stages but much simplier each stage. Schematic from somewhere:

I am so sorry to show schematics that i did not try myself, so please forgive if these have some flaws. :)

  Are you sure? yes | no

Yann Guidon / YGDES wrote 09/26/2017 at 22:18 point

oh, you mean to tune a LC tank to the desired frequency ? That's... not reliable enough in my book :-/

I couldn't make sense of all the circuits, they surprise me a lot and understanding them will take time... But it's a an interesting puzzle/challenge :-D

  Are you sure? yes | no

add_ocean wrote 09/26/2017 at 22:53 point

Putting this design into industry grade device will require high end, rock stable LC tanks, i suppose. And, i see it now, below 20 Hz it will be even less feasible as inductance rises, and not to mention core materials won't work fine at such low freq. :(

  Are you sure? yes | no

Yann Guidon / YGDES wrote 05/10/2016 at 12:41 point
I'm still "sourcing" transistors. Hundreds of AF137, G106T, AC125V, OC602, AF200...

And probably the weirdest : unmarked OC70, that look like it was made yesterday.

Apparently, "germanium is a thing" like vinyl LPs, factories seems to be restarted !

Anyway I have enough stock to work on 4T flip-flops.

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 13:32 point

ebay has a lot of similar stuff - I bought a bag of Russian MP-transistors which are the same germanium retro like 2N1xx. They have a nice "feature" - you can use pliers to deform its head and then you can remove it completely - inside it will be a bare P-N-P (or N-P-N) assembly that is LIGHT-SENSITIVE ;)

  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/03/2016 at 13:35 point

OMG ! I will try :-D

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 13:48 point

I remember article from soviet magazine for kids where authors built "solar panel" out of a few dozens opened MP-transistors that generated about 2V on sun ;)

P.S. I found it:

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 13:53 point

This is a table from the same article with experimental data about what single diode (two columns on the left) or single transistor (two columns on the right) can generate from light (voltage and current):

P.S. Full article:
Interesting fact that I didn't remember - author of this article is a woman :)

  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/03/2016 at 14:25 point

Awesome ! Thank you :-) I will certainly reuse this material so I'll need more infos :-)

If you have other "ideas" about them, please share ! For example I found this "logic gate"

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 14:51 point

Sure ;)

Another article series from the same soviet magazine was about building logic elements from those transistors (because they were very popular in Russia of 80s):

Here you can see NAND3 with open collector (блок А), NAND3 (блок Б) and trigger (блок В) that actually constructed from 2 NANDs:

  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/03/2016 at 15:02 point

@Alexander Shabarshin awesome, thank you !

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 15:19 point

And these accidental memories made me curious how fast such NANDs could run ;)

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 18:02 point

OK, I built it :)

It's MP25A p-n-p germanium transistor (similar to 2N189) manufactured in USSR in September 1979 (I got bunch of them from ebay relatively cheap) connected as 2nd circuit from article (NAND element), but instead of one diode V4 I put 3 silicon diodes connected in series (the circuit refused to work with 1 silicon diode as V4) and I use 10K resistors. According to spec MP25A should be able to work with frequencies up to 250 kHz, but this particular circuit has a limit about 10 kHz - see oscillograms for 5,10 and 20 kHz:

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 19:44 point

I put 4 diodes to the base circuit in order to shift threshold lower:

Then I put capacitor 480nF over the diode series and resistor from base to emitter 1K - as per @matseng 

and I got nice 100 kHz :)

P.S. Reducing voltage to 4V actually allowed 200 kHz signal to be processed:

and U-curve is more natural with 4V (threshold closer to U/2):

  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/03/2016 at 23:35 point

It seems we got a 2nd contributor here ;-)

I haven't received my eBay orders yet (it will take a while) so I hope that @Alexander Shabarshin will make a proper log page to describe these experiments :-)

Thanks for your precious time !

  Are you sure? yes | no

matseng wrote 04/03/2016 at 14:51 point

On the other hand any silicon BJT is also light sensitive. I remember cutting of the tops of TO3 encapsulated 2N3055's and using them as foto sensors when I was a teenager back in the late seventies.... I think that they actually generated quite a low of power in bright light.

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 14:54 point

These monster transistors are more difficult to open I assume...

  Are you sure? yes | no

jaromir.sukuba wrote 04/03/2016 at 18:24 point

Oh those yellowish scans from Russian magazines bring back the memories to five issues of Modelist-Konstruktor magazines I bought for 3 Slovak crowns (~= ten eurocents) from my schoolmate - back in 1993 - I was in third grade of elementary school. Funny thing is that I didn't understand a single word, I didn't even understand Russian alphabet. My father learned me it in one Sunday afternoon, so I could somehow read the articles (one in five Russian words resembles somehow equivalent Slovak word). That was the time when I got fascinated by electronics.

The M-K magazine had similar look & feel.

  Are you sure? yes | no

SHAOS wrote 04/03/2016 at 20:29 point

Yes, I remember Modelist-Konstruktor, but I don't remember any article from it :)

  Are you sure? yes | no

jaromir.sukuba wrote 04/03/2016 at 12:08 point

Having a bag of 500+ germanium switching transistors, this looks like the right pointless project for me!

  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/03/2016 at 12:55 point

are they for sale ? :-P

  Are you sure? yes | no

jaromir.sukuba wrote 04/03/2016 at 19:14 point

Don't ask hoarder to sell his sacremental ;-) though you can take a look at part of my collection

I must admit I'm slightly obsessed with germanium components.

  Are you sure? yes | no

Yann Guidon / YGDES wrote 04/04/2016 at 00:17 point

Well then thank you for your kind participation :-D

Would you like to use some of them to help with this project ? :-)

  Are you sure? yes | no

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