Germanium transistors: Difference between revisions
m (→Links) |
No edit summary |
||
| (One intermediate revision by one other user not shown) | |||
| Line 1: | Line 1: | ||
Many Tektronix scopes from the 1960's contain '''Germanium transistors''', e.g., [[OC170]], [[OC171]], [[2N1516]], and [[2N2207]]. | 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 | 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 | In most cases, germanium transistors can be replaced with modern general-purpose | ||
| Line 13: | Line 13: | ||
When a germanium transistor is used with its base-emitter junction DC coupled 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== | ==Links== | ||
Latest revision as of 03:11, 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)
