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3S76/Repairs: Difference between revisions
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==Germanium transistor replacement== | ==Germanium transistor replacement== | ||
The 3S76 contains eight 2N1516 and two 2N2207 PNP Ge transistors in | The 3S76 contains eight 2N1516 and two 2N2207 PNP Ge transistors in TO-7 packages. | ||
These transistors are prone to grow tin whiskers that tend to short random transistor elements to the case, eventually rendering it inoperative. | These transistors are prone to grow tin whiskers that tend to short random transistor elements to the case, eventually rendering it inoperative. | ||
One way to remove shorts due to tin whiskers is covered on the [[Germanium transistors/Repairs]] page, but a more durable solution is to replace the Ge transistors with Si | One way to remove shorts due to tin whiskers is covered on the [[Germanium transistors/Repairs]] page, but a more durable solution is to replace the Ge transistors with Si 2N3906s. | ||
This may require readjusting the Miller Levels and the Preamp Sensitivities for each channel, as well as the overall plugin gain. | This may require readjusting the Miller Levels and the Preamp Sensitivities for each channel, as well as the overall plugin gain. | ||
Dues to the long tailed biasing used in the 3S76, nothing else will need to be changed. | |||
The original TO-7 Ge transistors have 4 leads in a straight line, arranged C__SBE, where S stands for Shield and that lead has been cut off. | The original TO-7 Ge transistors have 4 leads in a straight line, arranged C__SBE, where S stands for Shield (the tin plated TO-7 case) and that lead has been cut off. | ||
The sockets for these transistors have 3 receptacles in a straight line, plus one offset to one side. | The sockets for these transistors have 3 receptacles in a straight line, plus one offset to one side. | ||
The center and offset | The center and offset socket receptacles were factory wired together under the chassis. | ||
A 2N3906 may be installed with its 3 leads installed in a straight line, with the flat of the TO-92 case facing the offset socket receptacle. | A 2N3906 may be installed with its 3 leads installed in a straight line, with the flat of the TO-92 case facing the offset socket receptacle. | ||
Alternatively, the center pin of the | Alternatively, the center pin of the 2N3906 can be offset toward the flat side of the package and inserted into the offset socket receptacle. | ||
The tripod arrangement may provide more mechanical stability, but its main advantage is that it assures correct installation. | The tripod arrangement may provide more mechanical stability, but its main advantage is that it assures correct installation. | ||
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I made a tool from a popsicle stick with a small hole just big enough to hold a TO-92 transistor. | I made a tool from a popsicle stick with a small hole just big enough to hold a TO-92 transistor. | ||
With this tool, I could reach into the space under the delay lines and position the 2N3906s | With this tool, I could reach into the space under the delay lines and position the 2N3906s above their sockets. | ||
A second stick or tool was used to press the transistor down into the socket. | A second stick or tool was used to press the transistor down into the socket. | ||