Why are vintage germanium transistors so big?

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jschussler
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Why are vintage germanium transistors so big?

Post by jschussler » Mon Sep 23, 2019 12:19 am

In the process of soldering and de-soldering and then resoldering some germaniums on my Strakal Brulu I accidentally killed them. Which is sorta tragic, since they were the Russian NOS you can't get any more.

But on the upside it gave me a chance to look inside:

(The dead ones next to some German versions, also NOS)
Image

The small one:
Image

The big one:
Image

I can sortof understand the size of the small one, but the tall one makes no sense. Why do we need 5x the space for the same size connection?

Anybody know?

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dot matrix madness
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Post by dot matrix madness » Mon Sep 23, 2019 2:22 am

The interior of these transistors shows that they were soldered by hand (under the microscope). Over time the required amount of substrate became smaller while keeping the larger can.
Licenced to solder since 1993

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JimY
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Post by JimY » Mon Sep 23, 2019 6:18 am

A big can helps isolate the device from ambient temperature - handy for Germanium because its so sensitive to heat. On the same tack, the taller can is better for attaching in a heatsink. Some old audio gear used individual heatsinks over the Ge transistor cans and you could buy them already pushed into a little aluminium block.

The long leads allow you to clip on a heatsink of some sort (sprung tweezers, aluminium hair grip or whatever metal thing you can clip on) to the leads near the case so soldering heat doesn't damage the internals which may have been assembled with a low melting point solder. And that's a good reason to continue using tin/lead solders for these - or sockets.

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Post by Jarno » Mon Sep 23, 2019 1:34 pm

Given that not 10 years earlier, the alternative was tubes/ valves, these were considered pretty tiny at the time :D

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JimY
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Post by JimY » Mon Sep 23, 2019 3:46 pm

Well, they did have the Nuvistor before then...
https://en.wikipedia.org/wiki/Nuvistor
Still needed heater power and that wasn't much less than conventional tubes like half a 12AU7 but it was a useful improvement when many were needed.
I built one from an old Tek oscilloscope into the front end of a low power tube amp. That Nuvistor is probably 40 years old by now.

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Re: Why are vintage germanium transistors so big?

Post by Synthiq » Mon Sep 23, 2019 5:08 pm

jschussler wrote:In the process of soldering and de-soldering and then resoldering some germaniums on my Strakal Brulu I accidentally killed them. Which is sorta tragic, since they were the Russian NOS you can't get any more.

But on the upside it gave me a chance to look inside:

(The dead ones next to some German versions, also NOS)
Image

The small one:
Image

The big one:
Image

I can sortof understand the size of the small one, but the tall one makes no sense. Why do we need 5x the space for the same size connection?

Anybody know?
Do you know if the two transistors have the same specs? My guess is that the big one can handle more current as the emitter(?) connection has a more substantial connection to be able to handle a larger current without burning up. Even the base(?) connection seems to have a thicker bond wire to be able to handle a larger base current. A large package would be able to dissipate more heat generated by the higher current.

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EATyourGUITAR
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Post by EATyourGUITAR » Mon Sep 23, 2019 5:26 pm

This was before anything with 2000 transistors was spec to fit in something the size of a small phone. I'm pretty sure there were smaller germanium transistor packages available at some point. Surface mounted soldering is very very old in aerospace and military applications.
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