[Guest]

I have just started to recap my 48-460 Hippo radio and I have a question about the line-to-chassis .2 cap. There are two ** with the notation "One of the leads of this capacitor is brought out appx 1/3 the total number of turns down from the outside foil so as to make it resonant with it's inductance at approx 455 kc." How am I going to replace this capacitor with a modern day equivalent?

[Ron Ramirez]

Hi Ray

These "special" capacitors are explained over at Chuck's fine site:

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

Most of us usually replace the "special" cap with a regular 0.22 uF metalized film cap and forget about it. These seem to work just fine as replacements with no ill effects that I am aware of.

[codefox1]

Been mentioned quite a few times. Evidently there were some marine beacons that operated close to the IF frequency many years ago, and this was an issue. Agreed, just replace the cap and you should be fine.

[exray]

Actually this is not a 'wavetrap' in the reception sense of the word. Philco apparently recognized that they were not bypassing IF frequencies to ground very effectively due to the inductance of the old foil wound caps. The solution was to add more inductance in series to 'tune' it to 455 for better bypassing at that frequency. Its all explained on Chuck's site.

Since modern caps don't have the same issue as the big old paper caps the coil is no longer required.

[codefox1]

Thanks, I think we can probably put this one to rest in perpituity.

[exray]

Doubtful It will always be confused with a real wavetrap at the front end that WAS intended to eliminate beacons and coastal stations. That issue has gone away too!