475M metal can caps


Bob Isselhard
 

I recently acquired a TEK 475M and purchased a hard-copy manual for it. I put the probe on channel A input and attached it to the calibrator. Then I moved the probe plug to channel B input. The amount of signal is correct (square wave, 300 MV) on either channel. I can not stabilize the trace however. It continues to slide to the left no matter where I move the TRIGGER SOURCE controls. I have only one probe so I can't exactly try the "connect both probes to the CALIBRATOR routine.

I checked the power supply voltages as per the manual and found the following:

+50 volts = +49.7 volts
+110 volts = +110.4 volts
+15 volts = +14.96 volts
+5.0 volts = +4.94 volts
-15 volts = -21.93 volts
-8 volts = -5.3 volts
UNREGULATED +50.volts = +64.3 volts

I looked at the large can caps and removed C1472, the filter cap across the diode bridge for the -15.0 volt supply. It actually looks good (3700 MFD, .47 ohms ESR).

Now the problem comes in. I have never worked with these before and did not realize there was an additional lug on the cap that was soldered to the lead that comes out on the other side of the board and is connected to the -15 volt test point.

I would like to obtain an exact replacement physical configuration-wise and re-solder the can lug to the test point and have it held down to the circuit board that way. However, if I can't find one, I can obtain a radial-lead, wired-in electrolytic and bridge the necessary connections. I wonder what to use to secure it to the metal piece adjacent to it? Hot glue? Super glue? Seal all? (one tube epoxy). I wonder what others have done here when replacing these large can caps? Granted, this one appears good, but why re-insert an old cap when I can replace it with a new one?

Any ideas gratefully accepted.

73, Bob K5INW

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