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My Humming squeeling motorboating Hippo 46-420 code 121 - Printable Version

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RE: My Humming squeeling motorboating Hippo 46-420 code 121 - apERNA1985 - 07-12-2026

Rod B this sounds like something I need. If this is caused by interference maybe it's enough to make my radio usable. For this one capacitor should I switch to something like a Sprague axial cap and then wrap around that or am I able to wrap the wire around the cap I'm using?

Paul I haven't tried an external antenna. Do you think this would help? Really I'd like to be able to use this radio and if there's nothing wrong with it, it's pretty much just a brick at this point. I'm kind of at the point where it's either going to become a glorified Bluetooth speaker or I'm just going to sell it on eBay. I'd really like to be able to actually use it.

I still have to run through the fixes/tests that Mrfixr55 recommended. But I'm out with my wife and the baby this morning so I haven't had a real chance to do anything yet

RE: My Humming squeeling motorboating Hippo 46-420 code 121 - radiorich - 07-12-2026

Hello apERNA185,
Yes, just like Mr. Fixxer said, I took an isolation transformer and one of those AC line filter networks with a computer-type socket, a light switch, and a single outlet , and mounted it into a nice project box. That’s what I run my AA5 sets off of, and it really helped with the noise.

Sincerely Richard

RE: My Humming squeeling motorboating Hippo 46-420 code 121 - RodB - 07-12-2026

All the coil needs is 8 turns of wire, the cap is used as a form for the coil. Remember, this is rf interference so unless there's a signal present to cause a heterodyne effect, you won't hear it.

Also, the coil is wired in series with the cap.

RE: My Humming squeeling motorboating Hippo 46-420 code 121 - Arran - 07-12-2026

That buzz is external to the radio, either it is RF interference or it's coming down the power line. I had a problem like that with some radios in my late Uncle's trailer, it was not a buzz as such but a sort of rhythmic noise almost like it was modulated, but for the past year I haven't heard it, in fact I haven't heard it since they replaced the nearby power pole. That noise coming out of the hippo sounds like a fluorescent light or a dimmer switch, though it could also be a defective transformer on the power pole.
Regards
Arran

RE: My Humming squeeling motorboating Hippo 46-420 code 121 - apERNA1985 - 07-16-2026

Hey guys I just wanted to follow up. I was going to restore the other chassis and see if it worked better, but I didn't have a 50B5 (mine uses 50L6) or an extra 35Z5. So I ordered a two pack of 35Z5s and a 50B5 off of eBay. I changed the 35Z5 in my restored chassis and the hum went from completely overpowering, sounding like Full throttle at a jet boat race to reasonable AM radio hum between stations, I got all the week stations back also. There is something wrong with the volume control, the radio never really gets quiet when you lower it down, and if you leave the knob at its lowest setting where it's resting against the switch to turn it off it starts to squeak like feedback in a microphone. If you jiggle the volume control just a little bit it goes away. I did try cleaning the volume control but it didn't seem to make a difference... I do intend to go through the radio and do more testing now that I could actually hear something in the upper part of the dial. I'm glad I got somewhere with this, I was at the point to give up the hobby, if I can't use AM radio in my house what good is a bunch of restored AM radios. I was thinking about just adding an auxiliary input to all of them and running Bluetooth through them.

RE: My Humming squeeling motorboating Hippo 46-420 code 121 - gary rabbitt - 07-24-2026

Coming to the party late. The noise I would bet 100% it is from a power line or something outside of the radio.  You will be chasing your tail around if you are trying to eliminate it from the radio. It's not being generated there you must go to the source.


The Philco Special Capacitor has a purpose as someone already said what it is for.  While you could use a plain cap and possibly not detect a difference, it was there to filter leftover IF that could leak into the B- and cause ringing, a howl or other weird behavior.
Lots online about the real reason for the Special capacitor.  And I have to say that cap/ filter is NOT to filter out the 500KC coastal stations that are now defunct.  THAT is a different wavetrap elsewhere in the RF section.

    Just a thought, take the Hippo to a friends house away from your neighborhood and give it a try.  I used to get the exact sounding buzz from a touch lamp when it was on. I don't know if they still have those things.