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3S76/Repairs: Difference between revisions
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(Explain using 2N3906s as replacements for most of the Ge transistors) |
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==Germanium transistor replacement== | |||
One way to remove shorts due to | The 3S76 contains eight 2N1516 and two 2N2207 PNP Ge transistors in a TO-7 package. | ||
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 2N3906. | |||
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. | ||
Nothing else should need to be changed. | Nothing else should need to be changed. | ||
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The center and offset pins were factory wired together under the chassis. | The center and offset pins were factory wired together under the chassis. | ||
A 2N3906 may be installed with | 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 2N3904 can be offset toward the flat side of the package and inserted into the offset socket receptacle. | Alternatively, the center pin of the 2N3904 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 | The tripod arrangement may provide more mechanical stability, but its main advantage is that it assures correct installation. | ||
Two of the TO-7 transistors to be replaced are under the delay line assembly and are ''extremely'' difficult to reach. | Two of the TO-7 transistors to be replaced are under the delay line assembly and are ''extremely'' difficult to reach. | ||
I have found that these are best installed with the leads in a straight line, using a pair of surgical forceps. | I have found that these are best installed with the leads in a straight line, using a pair of surgical forceps. | ||
It will be virtually impossible to install these transistors with your fingers. | It will be virtually impossible to install these transistors with your fingers. | ||
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 at their sockets. | With this tool, I could reach into the space under the delay lines and position the 2N3906s at their sockets. | ||
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Make SURE that each 2N3906 has all 3 leads securely installed in their correct receptacles, flat side facing the offset socket receptacle. | Make SURE that each 2N3906 has all 3 leads securely installed in their correct receptacles, flat side facing the offset socket receptacle. | ||
:-- [[User:Jadney|Jim Adney]] | |||