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Germanium transistors: Difference between revisions
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Many Tektronix scopes from the 1960's contain '''Germanium transistors''', e.g., [[OC170]], [[OC171]]. | Many Tektronix scopes from the 1960's contain '''Germanium transistors''', e.g., [[OC170]], [[OC171]]. | ||
These transistors are prone to failure. | These transistors are prone to failure. One particular failure mechanism is the growth of tin whiskers from the tin-coated inside walls of the transistor case. | ||
In most cases, | In most cases, germanium transistors can be replaced with modern general-purpose | ||
silicon bipolar transistors with no modification to the circuit. | silicon bipolar transistors with no modification to the circuit. | ||
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(differential amplifier, Schmitt trigger) change the pair, not just one transistor. | (differential amplifier, Schmitt trigger) change the pair, not just one transistor. | ||
When a germanium transistor is used with its base-emitter junction in parallel with | When a germanium transistor is used with its base-emitter junction DC coupled in parallel with | ||
a germanium tunnel diode, you cannot simply replace the germanium transistor with silicon. | a germanium tunnel diode, you cannot simply replace the germanium transistor with silicon. | ||
It will not work because the "high state" voltage across the tunnel diode will not | It will not work because the "high state" voltage across the tunnel diode will not | ||
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==Links== | ==Links== | ||
* [https://nepp.nasa.gov/whisker/anecdote/af114-transistor/index.html Tin whiskers inside AF114 transistors] / [https://nepp.nasa.gov/whisker/anecdote/af114-transistor/2005-Brusse-tin-whiskers-AF114-transistors.pdf Presentation] − NASA Electronic Parts and Packaging (NEPP)] | |||
* [https://groups.io/g/TekScopes/message/35340 321A 2N2207 transistor replacement] | |||
* [https://www.vintage-radio.net/forum/showthread.php?t=5058 Thread on tin whiskers in OC170/OC171 @ vintage-radio.net] / [https://www.vintage-radio.net/forum/showthread.php?t=35171 Detail pictures] | * [https://www.vintage-radio.net/forum/showthread.php?t=5058 Thread on tin whiskers in OC170/OC171 @ vintage-radio.net] / [https://www.vintage-radio.net/forum/showthread.php?t=35171 Detail pictures] | ||
==Pictures== | |||
<gallery> | |||
Tin whiskers 001.jpg | Tin whiskers in AF114 case (from nepp.nasa.gov) | |||
Tin whiskers 002.jpg | Tin whiskers in AF114 case (from nepp.nasa.gov) | |||
Tin whiskers 003.jpg | Tin whiskers in AF114 case (from nepp.nasa.gov) | |||
Tin whiskers 004.jpg | Tin whiskers in AF114 case (from nepp.nasa.gov) | |||
</gallery> | |||
[[Category:Transistors]] | [[Category:Transistors]] | ||
[[Category:Repair issues]] | [[Category:Repair issues]] | ||