Advice from a germanium specialist

A project log for Germanium ECL

How fast can germanium transistors compute ? And how much current will that draw ?

Yann Guidon / YGDESYann Guidon / YGDES 12/21/2016 at 19:5615 Comments

Is there anything to be careful about, when dealing with Ge transistors ?

According to a retired engineer, soldering is tricky. I know Ge is very temperature-sensitive but he advised to not cut the leads. I'm still not sure about the exact meaning but Ge transistors can easily get destroyed during soldering. The soldering iron should be set to the lowest possible temperature, and I will find a way to cool the part down before and immediately after the joint is made...

Who else can share their precious advices ?

Now I get it why transistors were socketed back in the days...

And this might be a solution. High frequency signals require short leads and the transistors should barely sit above the PCB plane to keep lengths and traces as short as possible. I'll have to find thousands of individual female sockets that I solder in the PCB holes. I have a "small" stock, maybe a thousand of them, but that is far from enough for a whole system...

(picture found on eBay)

I use these a lot to make prototypes, they are very handy. Unfortunately, all I can find (yet) is small sockets assembled in one (or two) row with 2.54mm spacing. Any hint for where to find individual pins ?

Furthermore, I would cut the smaller end because the larger socket part would go through the PCB. That's a lot to cut...


I have about 4K receptacles of this kind:

First problem : I only have 4K. The AF240 has 4 pins so that's only enough for 1K transistors (barely enough for the register set alone). I got at least 8K AF240 (see below to see how it looks like) so I'd need a crazy 32K receptacles!

Second problem : To get enough receptacles, I'd have to spend about $200 (that's chinese dollars, you know, you get what you pay for...)

Third problem : Reliability. The transistor doesn't move much but... multiplied by 8K, it's a recipe for catastrophe ! I should rather make small modules with a dozen of transistors and test them well (eventually replace a failed part).

Using receptacles, a vibration, a mishandling or any physical influence could perturbate the circuit, making it hard to use. I'd rather damage a few transistors before use, than spend all my time guessing with can got slightly upset...

Concerning soldering : I did some research of the "mesa" technology and it does not seem to be particularly fragile (compared to others) so I'll make a bet by carefully soldering.


add_ocean wrote 09/26/2017 at 02:32 point

Best idea is to forget sockets and tweezers at all. Because of cost, reliability, and complexity. Besides, locking forceps might crack the glass insulators, and oxygen begin slowly destroy junctions.

Leads should be left 8-10 mm length, use iron of 25 W, solder briefly for 1 second, and allow to cool 5 seconds between touching each lead. That will ensure dices never get hotter than maybe 100C during solder.

Testing (measuring) each transistor carefully before putting on board saves plenty time on latter troubleshooting  :)

Danger of overheat is the case of very old and "barely alive" germaniums, the dream of archeologist. Then long leads and/or copper tweezers can help, but with great care to insulators.

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Yann Guidon / YGDES wrote 09/26/2017 at 02:46 point


just like with the RES15 I should also make a tester for the germaniums... My TODO list has already exploded however :-/

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tombrend wrote 12/22/2016 at 19:32 point

Those look like Mill-Max receptacles.

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Yann Guidon / YGDES wrote 12/22/2016 at 20:18 point

yes. Given 8K transistors (evaluated), that's 32K receptacles... That would be a crazy bulk order...

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tombrend wrote 12/22/2016 at 20:24 point

Yep- and they're probably not as cheap as you'd like. Mouser pricing only gets down to 0.56 at 1k for the 0405-0-15-80-34-80-04-0

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Jean THOMAS wrote 12/22/2016 at 13:09 point

I remember someone saying that he used cold spray to cool his transistor while soldering it. Rémy from Sonelec-Musique uses single row machined ic socket as transistor sockets.

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Yann Guidon / YGDES wrote 12/22/2016 at 18:20 point

In the case of the AF240 (and its siblings), there are 4 pins so I would use dual-row sockets such as 

It seems to be more practical than individual pins (they would stay together) and the strip can be cut in different lengths (even 2)

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Yann Guidon / YGDES wrote 12/22/2016 at 00:31 point

While we're here, can somebody explain the purpose of the 4th pin ?

It's connected to the metal can, should I just ground it ? Leave it unconnected ? Any risk of stray capacitance ?

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K.C. Lee wrote 12/22/2016 at 00:07 point

Get yourself a pair of locking forceps.  You can clamp on the leads between the solder joint and the "can" and use that as a heatsink.

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Yann Guidon / YGDES wrote 12/22/2016 at 00:13 point

I'm not sure it's both enough and practical... I'll try and see.

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K.C. Lee wrote 12/22/2016 at 00:17 point

I have soldered a few germanium with an 40W iron (without temperature control) nor knowing the heat damage issue back when I started out. Never had an issue.

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Yann Guidon / YGDES wrote 12/22/2016 at 00:30 point

Considering the price of the transistors I'll use, the quantity I'm about to receive and the modularity of the system (small PCBs with maybe a dozen of Ge's)... I'll probably just solder and check the module's health.

"AF 240 is a germanium PNP mesa transistor" though I'm not sure what kind of process this is (it's not epitaxial yet ?)

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Yann Guidon / YGDES wrote 12/22/2016 at 00:13 point

and the AF240 have 4 pins so it's going to be... tricky to use :-/

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Thomas wrote 12/22/2016 at 07:14 point

I remember reading about the "thermal clamp" method in a 60s electronics textbook *). If I remember right, the tool in the illustration had a small rounded bar of copper perpendicular the leads. Not sure how they avoided bending the leads too much. From my "electronics scavenging" days I remember the UHF radio tuners used to have germanium transistors, and those sometimes were hand soldered, too The leads were rather short (to reduce inductance) .
*) No, I'm not that old. The electronics section in the public library just had rather old books.

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Yann Guidon / YGDES wrote 12/22/2016 at 20:15 point

I used to learn electronics as a kid by looking at old books in the public library too :-)

I'll have to see the practicality of thermal clamps...

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