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48-460 squeal - Printable Version

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48-460 squeal - Eric Adams - 03-20-2014

Hi guys,
I just did a recap on this Hippo. I even replaced most of the mica caps as well as a good amount of out of range resistors. The tubes have been tested and I replaced 2 of them. Performed an alignment.
Reception is great but between stations there is a VERY noticeable squeal. Any ideas where to look?

http://www.nostalgiaair.org/Resources/634/M0013634.htm

Thanks

RE: 48-460 squeal - murf - 03-20-2014

I have run into this before, and have been able to get rid of it by fine tuning the alignment.
murf

RE: 48-460 squeal - Ron Ramirez - 03-20-2014

Is your loop antenna properly connected? If one wire is disconnected, the set will squeal, howl, buzz, and in general not play correctly.

RE: 48-460 squeal - Chuck Schwark - 03-20-2014

If your loop is connected you may also try a slight stagger-tune of the I.F.'s as suggested above.

Chuck

RE: 48-460 squeal - Eric Adams - 03-20-2014

It came with no antenna. The loop is connected but it is from what I think was a 46-250. Would that make the difference? If so what can be done to correct this?

RE: 48-460 squeal - morzh - 03-20-2014

If it squeals on you tell it it is not an honorable thing to do.
And make sure it is loop and not a noose Icon_smile

Now on teh seriuous note, I only have the sch for 48-620, but if it is also an AC/DC set, there is a capacitor or a capacitor in series with small inductance conencting the electrical common and RF common (chassis). If this cap or inductor are bad the radio will misbehave including squealing, howling, roaring, motorboating and occasionally uttering some bad words on its own at which point you should turn it off, pull the belt from your pants, give it a good threshing and then inspect for bad parts and re-align.

RE: 48-460 squeal - Eric Adams - 03-20-2014

OK Morzh, here is the schematic for the 48-460

48-460

Would it be C5?

RE: 48-460 squeal - Eric Adams - 03-20-2014

Something else that I just discovered: With the antenna disconnected I get a soft high pitched squeal that changes with volume but doesn't change with movement of the tuning cap.

RE: 48-460 squeal - morzh - 03-20-2014

No. C19.

But C5 is also worth checking as without it the antenna will simply not work.

RE: 48-460 squeal - Eric Adams - 03-20-2014

C5 is new. Any idea why there is a soft squeal with no antenna connected?

RE: 48-460 squeal - morzh - 03-20-2014

Is C19 new or is it even there?

RE: 48-460 squeal - Eric Adams - 03-20-2014

Yes it is there. I have 2 schematics. This one shows a .2mf and the other shows a .5mf. I used a .5 because that is what was in there. It didn't have the wire wrapped around it. I don't think that is needed anymore. Is it?

RE: 48-460 squeal - morzh - 03-20-2014

Did it have a wire wrapped around it before?
0.2uF or 0.5uF does not matter, it is an RF link cap between the two commons, either will work fine.

RE: 48-460 squeal - Eric Adams - 03-21-2014

No wire, so I tried one. No change.

RE: 48-460 squeal - Jamie - 03-21-2014

Hippos usually have rubber wiring. Did you replace any wires, or cover them with heat shrink? If so, check the routing of the wires. Sometimes solving a squeal is as simple as moving a wire 1/4 inch. If this isn't the trouble, i think your alignment might be a little too "hot". Like Chuck said, un-align it a little and see if the squeal stops.