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Germanium lemonade

A project log for Clockwork germanium

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

Yann Guidon / YGDESYann Guidon / YGDES 03/08/2020 at 05:350 Comments

"When life gives you lemons, make lemonade" they say. This whole project is about "how did they manage to make lemonade back in the days ?"

To understand this, I explore the old technology and parts "from back then". In this page I try to evaluate the quality and variance of the 70+ OC139 of my stock.

They come from two sources and I was curious : do they come from the same batch ? Have they been already binned ? How much do they differ ? Is the leakage so bad ?

The OC139 seem to be really "vintage", looking at the oxidation of the leads. Date code seems to be around 1961.

Measuring the leakage is a pretty big deal because it badly affects the gain displayed by simple hFEmeters. Look at http://www.geofex.com/Article_Folders/ffselect.htm for the extended explanations.

I didn't use my multimeter this time, but a handy little Chinese-made tool that guesses the type of tripole and its characteristics, which I wrote below.

I bought this device at a local store with the usual markup (welcome to France) but I needed it to test my old capacitors and it has other useful features so I didn't care that much. And it was sold by an old, reputable store :-)

The gain itself is not a big issue, as long as it's about > 20 and there is no point if it is >40 for this specific application. It's also good to see which parts are real lemons and should not be used in a circuit. For example, too high a leakage will disrupt my circuits. We have totally forgotten to take leakage into account in this century !

Measuring these parameters is not an exact science since germanium is very sensitive to heat (even from the fingers) and even to light (the black paint can't stop all the light if it's intense enough) so sometimes I had to make several measurements.

minifux1 :

hFE Vbe Ice0
106 210 5
34 224
31 204 7
156 219 1
193 21 164
???

36 232
29 229
36 248
32 132
30 115 14
44 167 14
40 195 7
32 239
36 131 1
120 195 7
46 215
86 200 7
26 213
38 210
33 268
31 219
48 124 4
49 195 14
21 210
30 200 7
22 224
31219 14
173 161 35
26 205 5

ampliatubes:

hFE Vbe (mV) leak (µA)
40 126 4
59 205 7
42 220
37 200 14
23 221 8
34 214 14
42 219
24 232 1100
26 213 5
34 229
34 220 1
28 216
26 215
40 204 7
?? 196 200
79 197 8
33 124 5
95 220
73 155 14
49 215
29 233 14
44 137
134 214 7
124 159 8
28 210 2
46 229
220 156 35
37 211
31 133
42 204 14
46 222 4
296?? 218 11
424
188
35
40
205
7
90
126
7
52
205
7
46
135
2
31
220

464
194
34
223
174
28
22
224

26
220

72
200
5

Verdict : one totally rotten lemon, several in bad shape, most are bitter but usable, but some have interesting characteristics and demand more examinations. Is their high gain real or an artefact ? and if they really have such a high gain, can they be used for more noble purposes than digital switching ?

I also wonder about those parts with Vbe < 200mV.

I didn't/couldn't check for the gain-bandwidth product (or rise and fall time). That should be for another time and for the high frequency dividers :-D

I guess about half of them would be used for the intended circuit (the shift registers, I need gains between 20 and 40 and no significant leakage). I might have to get more of them to complete the circuit because there are quite a lot of stages... but they have become so expensive !

Next step would be to plot the data in a graph and re-bin the stock, according to the various groups I identify in the dot cloud.

And yes, germanium is fun but silicon is so much better :-D I measure so little relative variations in new parts, even cheap ones...

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