49-901 Capacitor and coil combination missing - Printable Version

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+--- Thread: 49-901 Capacitor and coil combination missing (/showthread.php?tid=1152)

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49-901 Capacitor and coil combination missing - davemc - 05-25-2008

I am restoring a Philco 49-901. It is all original EXCEPT that C303 (in Beitmans schematic) has been replaced with a .1uf 600 volt orange drop. The schematic shows an associated coil in series with the capacitor. I recall restoring a 42-xxx Philco which also had this part. In that case I just wound the same number of turns around a new film capacitor (the original wiring was rubber and falling apart). This part is connected between B- and the chassis, in parallel with a 150K resistor.

Does this coil have any real function? If so, does anyone know how many turns of wire I should use (since the part is missing in my radio)?

Thanks

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- exray - 05-25-2008

They attempted to 'tune' this bypass arrangement for the most effective bypassing at the IF frequency. Some of the older paper caps showed resonance on other frequencies because of their internal construction and didn't perform well at 455 so the goal was to tune that back down to 455.

Modern caps are not particularly known for this problem so the coil can be omitted. Unless you just want it there for looks but then you theoretically run the possibility of recreating the original problem unless you know the internal inductance of the new cap and can calculate it in accordingly.


-Bill

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- Chuck Schwark - 05-25-2008

The coil/cap in series did have a function, but can be just a cap now.

See my Service Tip: http://www.philcorepairbench.com/tips/svctip37.htm

Chuck

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