I have started working on a Philco 49-500, 5-tube AM model. The Riders schematic shows that one of the paper capacitors, C304, includes an internal coil in series with the 0.1 cap. All of the original capacitors are in the radio. This one is marked "Special". It has only the typical, two axial connections, no coil connection off to one side. What does this coil do? Can this cap/coil be replaced with a normal modern cap of the same value (but without the coil)?
Thanks,
Robert H.

Robert: C304, along with the coil, is a wavetrap to keep old maritime stations from interfering with the IF. No longer required - you can eliminate C304 altogether. Or leave it there if you like.
Doug

:I have started working on a Philco 49-500, 5-tube AM model. The Riders schematic shows that one of the paper capacitors, C304, includes an internal coil in series with the 0.1 cap. All of the original capacitors are in the radio. This one is marked "Special". It has only the typical, two axial connections, no coil connection off to one side. What does this coil do? Can this cap/coil be replaced with a normal modern cap of the same value (but without the coil)?
:Thanks,
:Robert H.

Thanks, Doug.
Robert H.

:Robert: C304, along with the coil, is a wavetrap to keep old maritime stations from interfering with the IF. No longer required - you can eliminate C304 altogether. Or leave it there if you like.
:Doug
:
::I have started working on a Philco 49-500, 5-tube AM model. The Riders schematic shows that one of the paper capacitors, C304, includes an internal coil in series with the 0.1 cap. All of the original capacitors are in the radio. This one is marked "Special". It has only the typical, two axial connections, no coil connection off to one side. What does this coil do? Can this cap/coil be replaced with a normal modern cap of the same value (but without the coil)?
::Thanks,
::Robert H.

I find that the wavetrap can remove other interference as well, and can prevent feedback between the antenna and the radio.

T.

This is not a wavetrap to keep maritime radio from interfering,these will be found in the antenna circuit.

This is a tuned circuit to keep the IF off of the B-. You can replace it with a regular capacitor but if you end up with a squeeling radio you know where to look.

These are easy to make by winding a few turns of wire on the capacitor and tuning it with a signal generator and a scope.

Dave

Ah..........always helps to look at the schematic. Nice idea.......and typical of Philco, too. I wonder which company was better--Philco or Zenith. They both certainly made nice sets. I shouldn't start that, though. We could have another mile long thread regarding which company was the best.

T.

.........But I'm looking at the schematic, and I notice that the wave trap go from B- to the 'floating' chassis. What is the purpose here? Same thing?

T.

In addition to replacing all electrolytic & paper capacitors I also replaced this "Special" capacitor with a regular film cap of the same value. Also had to adapt an on-hand salvaged speaker to this radio since the original speaker cone had been shredded. The radio came to life and seems to be working normally, without noticeable hum or other problems. Guess that I was lucky.

I did perform and "autopsy" on the Special capacitor, but found no sign of a coil inside, just the usual paper & foil roll.

Check this link for information on the special capacitor.

http://www.philcorepairbench.com/tips/svctip37.htm

Dave

:Check this link for information on the special capacitor.
:
:http://www.philcorepairbench.com/tips/svctip37.htm
:
:Dave

That link certainly explains why there was no separate coil in the "Special" capacitor. Thanks, Dave.
Robert