Before I can proceed with the debouncing circuit, I have to evaluate the characteristics of the transistors and choose the lousiest (debouncing is not a critical circuit). Fortunately I had built a board for manually Testing Germanium transistors.

Remark: the gain and leakage are tested at 10V but this clock works betwwen 4 and 5V. I had expected leakage to be exponential but it appears to be logarithmic vs voltage... so the values will not change much in practice. The leakage moves (drops during the measurement) quickly too, and it very sensitive to temperature, which is disconcerting. I suppose that the large variations are due to the varying time to manipulate them with warm fingers, varying times to measure, etc.

Oh and gain seems to decrease with temperature... spooky...

I have no experience yet to deal with leakage so I don't know how to proof my circuits against it (and low gain). I would expect a minimum gain of 20 so I can have some margin with a 1:10 resistor ratio for the feedback.

Additionally, leakage seems to be a major obstacle to low power consumption and I hope to get some skills with this design.

Let's now pick 10 MP13 and 10 MP26 at random and test them:

МП13Б (MP13B) :

Off (mV)	On (mV)	Leakage (µA)	Gain
108, 83	516, 470	43, 33	40.8, 38.7
310, 260, 220, 200	770, 705, 640, 623	125, 105, 88, 81	46, 44.5, 42, 42,3
220, 200, 180, 160	640, 608, 580, 543	88, 81, 73, 64	42, 40.8, 40, 38.3
330, 280, 200	740, 680, 580	133, 113, 81	41, 40, 38
230, 200, 180, 160, 100	555, 517, 490, 460, 372	93, 81, 73, 64, 40	32.5, 31.7, 310, 30, 27.2
250, 210, 180	750, 690, 650	101, 85, 73	50, 48, 47
250, 100, 85, 66 (i've left it cool a while)	660, 392, 372, 339	101, 40, 34, 26	41, 29.2, 28.7, 27.3
350, 280, 220	790, 700, 620	141, 113, 88	44, 42, 40
220, 200, 160	645, 613, 560	88, 81, 64	42.5, 41.3, 40
230, 200, 180, 130	615, 575, 515, 472	93, 81, 73	38.5, 37.5, 33.5, 34.2

МП26А (MP26A):

Off (mV)	On (mV)	Leakage (µA)	Gain
350, 300, 270	560, 500, 470	141, 121, 109	21, 20, 20
600, 500, 400	880, 780, 660	243, 202, 161	28, 28, 26
230, 210	407, 385	93, 85	17.7, 17.5
360, 320, 250	590, 550, 470	145, 129, 101	23, 23, 22
210, 190	450, 427	85, 77	24, 23.7
240, 210	465, 428	97, 85	22.5, 21.8
300, 250, 200	500, 420, 363	121, 101, 81	20, 17, 16.3
220, 200, 190	413, 390, 378	88, 81, 77	19.3, 19, 18.8
430, 400, 300, 250	630, 600, 480, 430	173, 161, 121, 101	20, 20, 18, 18
470, 400, 300	725, 646, 531	190, 161, 121	25.5, 24.6, 23.1

As you can see, I don't use spreadsheets. I am THAT oldschool. Though I might try to import that in gnuplot, who knows.

Now the most interesting part : МП26А's gain is about 20 and МП13Б is about 40. From the reference number I would have expected the reverse... Once again, it was important to measure !

Alexander confirmed: "without suffix it's 12, with suffix 20...60"

So I wanted to pick the "lousiest" and the МП26А (about 75pc) is selected for the debouncer.

At "room temperature", the leakage is not excessive but 100µA is still much more than what's needed to run a quartz oscillator or other things we take for granted in the CMOS era...

Question : is gain correlated with leakage ? Should I select high or low gain transistors then ? Since the temperature varies widely, it's hard to sort parts by leakage, but I should see if the gain has a positive influence...

SHAOS provided more insight:

info about some transistors : http://zhurnalko.net/=sam/junyj-tehnik-dlja-umelyh-ruk/1985-10--num5

MP13 is not here - strange. I found it separately:http://www.eandc.ru/catalog/detail.php?ID=12249

and this is about MP26:http://www.eandc.ru/catalog/detail.php?ID=12278
for МП26А it's 20...50
for Б it's higher - 30...80
so it looks like without letter it is a trash and higher letter means better gain :)

page about diodes: http://zhurnalko.net/=sam/junyj-tehnik-dlja-umelyh-ruk/1985-10--num4

(I don't understand russian, BTW :-D)

I also got 10×GC117C. The leakage seems to be lower. 2 parts are dead and the gains are all over the place: 37, 62, 50, 60, 50, 75, 36, 60. Now I understand why "matched pairs of Germanium transistors" was such a thing.

They seem to be a better fit for a Xtal oscillator but I still wonder if the gain is high enough...

For the record:

GC117c low noise PNP RFT

Ge PNP 20V 50mA 70mW F < 10dB

According to http://www.radiomuseum.org/tubes/tube_gc117.html:
Introduced in 1963, made by RFT/HFO/VEB (germany), similar to OC817 (300KHz max)

Discussions

add_ocean wrote 09/26/2017 at 22:10

I know reverse base-collector current, it rarely reaches 5 microamps for all those МП at room temp., so putting 10K resistor between base and emitter makes transistor to be reliably closed, zero leakage. Are we going to leave base floating in the air?

Secondly, gain should be measured under rated collector current, and less current renders much lower gain in case if Ge.

Amplification Ge rated at 1 mA usually, but UHF or switching transistors can be rated at 5 or even 25 mA. МП26А rated at 2,5 mA, btw. (i previously mentioned here 25mA but sorry, checked again, its МП20 and 21 amplification rated at 25 mA). Most trusted book for these is by Goryunov, nothing else.

Are you sure? yes | no

Yann Guidon / YGDES wrote 09/26/2017 at 22:16

that's good to know, spacibo :-)

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Testing Germanium transistors (2nd part)

GC117c low noise PNP RFT

2nd approach

Crystal Oscillator (Germanium Edition)

Discussions

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