Germanium transistors: Difference between revisions
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Many Tektronix scopes from the 1960's contain | Many Tektronix scopes from the 1960's contain '''Germanium transistors''' in the TO-7 package, e.g., [[OC170]], [[OC171]], [[2N1516]], and [[2N2207]]. | ||
These transistors are prone to failure. | |||
In most cases, | These transistors are prone to failure. One particular failure mechanism is the growth of tin whiskers from the tin-coated inside walls of the TO-7 case. | ||
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. | ||
Reasonable silicon replacements for small-signal NPN and PNP | Reasonable silicon replacements for small-signal NPN and PNP | ||
germanium transistors are 2N3904 and 2N3906, respectively. | germanium transistors are the 2N3904 and 2N3906, respectively. | ||
When transistors appear in pairs in the original circuit | When transistors appear in pairs in the original circuit | ||
(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 | ||
be enough to turn on the transistor. If a germanium transistor in this type of circuit | be enough to turn on the transistor. If a germanium transistor in this type of circuit | ||
fails, you either have to find a working replacement germanium transistor or modify the | fails, you either have to find a working replacement germanium transistor or modify the | ||
circuit to work with a silicon transistor. | circuit to work with a silicon transistor. | ||
Click on the '''Repairs''' tab above for one possible method for eliminating internal Tin whisker shorts. | |||
==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 Detailed analysis 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] | |||
==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]] | ||
Latest revision as of 04:11, 7 March 2024
Many Tektronix scopes from the 1960's contain Germanium transistors in the TO-7 package, e.g., OC170, OC171, 2N1516, and 2N2207.
These transistors are prone to failure. One particular failure mechanism is the growth of tin whiskers from the tin-coated inside walls of the TO-7 case.
In most cases, germanium transistors can be replaced with modern general-purpose silicon bipolar transistors with no modification to the circuit.
Reasonable silicon replacements for small-signal NPN and PNP germanium transistors are the 2N3904 and 2N3906, respectively.
When transistors appear in pairs in the original circuit (differential amplifier, Schmitt trigger) change the pair, not just one transistor.
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. It will not work because the "high state" voltage across the tunnel diode will not be enough to turn on the transistor. If a germanium transistor in this type of circuit fails, you either have to find a working replacement germanium transistor or modify the circuit to work with a silicon transistor.
Click on the Repairs tab above for one possible method for eliminating internal Tin whisker shorts.
Links
- Tin whiskers inside AF114 transistors / Detailed analysis presentation − NASA Electronic Parts and Packaging (NEPP)
- 321A 2N2207 transistor replacement
- Thread on tin whiskers in OC170/OC171 @ vintage-radio.net / Detail pictures
Pictures
-
Tin whiskers in AF114 case (from nepp.nasa.gov)
-
Tin whiskers in AF114 case (from nepp.nasa.gov)
-
Tin whiskers in AF114 case (from nepp.nasa.gov)
-
Tin whiskers in AF114 case (from nepp.nasa.gov)
