Vintage transistors and tin whiskers

Cursitor Doom wrote in news:r9rgu3$h74$ snipped-for-privacy@dont-email.me:

Put it in your ten below freezer for an hour and let the cold disintegrate the non alloyed tin.

Then give it a nice hard rap to break it all loosed like we used to do to the old tube type TVs to get them going again.

Kidding of course... except for the TV thing. That worked. So did taking the back off it and re-seating all the socketed tubes and components. Worked every time. It is almost always a mechanical connection.

I don't know about the whiskers but Ge transistors have high leakage and no sharp knee at low currents. I wonder if 10 ohms is too low depending on the voltage applied by your meter. I have a few of the later AC188 types. I'll dig them up tomorrow and measure their resistances.

For quick go-no go checks of transistors, I prefer analog MMs. The static forward resistance depends highly on the current applied through the probes.

I used to have some OC71s and OC72s a long time ago. They made neat phototransistors with the paint scraped off from their glass enclosures.

OK, I got the AC188s. With a DMM they measure 25-50 ohms forward and a few Ks in the reverse direction.

I think you've misunderstood the problem here, Pimpom. The leakage in question is between the case ("screen") and the die and significantly pre- date the black-painted phototransistors we all fondly recall from 50 years ago. :-)

I have had some success with an Eddystone EB35 by replacing them with silicon transistors and adjusting the base bias to get approximately the same collector current.

(I was a tester on the production line at Eddystones when EB35s were going through, so I am the one to blame if they don't meet spec.)

If the Tin Man in the Wizzard of Oz tried to grow a beard, they would be really big tin whiskers. ;-)

I have 4 ECG160 transistors (2 that are unused and 2 that look like they may have been used to test something). Send me your address and I'll send them along if you think that these will resolve your problem. I doubt that I will ever use these.

Dan

Thanks for the advice and offers of parts, guys; much appreciated. On reflection I decided to replace with silicon. The purists would go to the trouble of hollowing out the old transitors and fitting the silicons inside them. Fortunately, I'm no purist. :-D

And if something starts oscillating because you have too much gain with the silicon replacements then adding a low value R in series with their emitters will usually fix.

No problems here. If you want to use the ECGs to verify that everything works prior to "upgrading" to Si, the parts are available. These are small enough that they will fit into a small padded envelope, so shipping will be next to nothing.

Let me know if you want them (no charge). Dan

Thanks Dan, much appreciated.

There are already emitter resistors, but they are bypassed, so adding resistance in series with the bypass capacitors (or removing them altogether) would be the way to go.

I used fairly mundane silicon transistors with a lowish cutoff frequency and didn't have any trouble.

Retrofitting germanium transistor circuits can be tricky, especially the ones where they rely on the apparent beta being negative, i.e. the CB leakage being larger than I_C/(true beta).

Cheers

Phil Hobbs

These were relatively late germanium technology (0C171) with a high ft and internal screen, so they didn't need the external neutralising network of the earlier germanium types. That encouraged me to try a direct substitution which only needed some adjustment of the base biasing network.

Does anyone still make ge transistors? I can't think of any use for them.

The only production ge devices I know of (excepting SiGe) are back diodes, which I think are the only germanium parts fabricated using lithography.

John Larkin wrote in news: snipped-for-privacy@4ax.com:

General Electric? Hehehe.. You mean Ge as in Germanium.

Ge makes good photodiodes for some uses. They're very leaky, but if you make the epi thin enough, they can cover 350-1800 nm, which otherwise requires expensive stacked-die devices. Garden-variety ones are more like ordinary InGaAs, i.e. 800-1800 nm, which is much less interesting.

Cheers

Phil Hobbs

John Larkin wrote in news: snipped-for-privacy@4ax.com:

Also as a side note to the title of this entire thread...

'Vintage transistors' were NOT 'tin plated' like todays parts are. They were Nickel Cadmium plated. A far superior plating but with carcinogenic dangers that caused Cadmium and Cadmium alloys to be banned. But you can still buy, eat and die from Beryllium parts.

Phil Hobbs wrote in news: snipped-for-privacy@electrooptical.net: