emerson: Ch= 120372B; 883B

 Radio has hum and distortion in the sound. CK all tubes  cleaned chassis. Any help   

                                                                                 Thanks  Merl

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Dear Merlin,

The most common cause of hum is bad electrolytic filter capacitors in the power supply.  In this radio, there are two such capacitors, C9 and C10 as shown on the schematic.  C9 and C10 are likely contained in a single aluminum can or paper cylinder.  If you replace those with new electrolytic capacitors, your hum will likely disappear.  The distortion may also be eliminated.

If the distortion persists, any paper capacitors in the radio would be suspects worthy of checking and replacing.  Also, this radio has a primitive integrated circuit called a "couplate" which looks like a rectangular ceramic capacitor, but with 7 leads.  The circuit diagram shows the parts inside this "integrated circuit," which you can reconstruct from individual components if necessary.  In particular, if the capacitor labeled C6 inside the couplate has high leakage current, it could cause distortion.  To check whether this capacitor has high leakage, simply check the voltage on the grid of the output tube (pin 2 of the 50C5).  If it is near 0.4 volts as shown on the schematic, and the cathode is near 6 volts, then C6 is not showing high leakage.  If either of those two voltages is significantly higher, that would be a sign of leakage in C6.

There can be other causes of distortion, which we can follow up on later if the above advice doesn't solve the problem.

Best regards,

Tom

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 Thanks will try your input and get back to you   Merl

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Since the last post is not a question, let's allow this thread to circulate out of the forum current listings.

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