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?
Posts: 13,776
Threads: 580
Joined: Sep 2005
City: Ferdinand
State, Province, Country: Indiana
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.
--
Ron Ramirez
Ferdinand IN
Posts: 2,128
Threads: 18
Joined: Oct 2008
City: Merrick, Long Island, NY
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.
Posts: 893
Threads: 9
Joined: Mar 2008
City: Vieques, PR USA
State, Province, Country: PR
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.
Posts: 2,128
Threads: 18
Joined: Oct 2008
City: Merrick, Long Island, NY
Thanks, I think we can probably put this one to rest in perpituity.
Posts: 893
Threads: 9
Joined: Mar 2008
City: Vieques, PR USA
State, Province, Country: PR
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!