Brunswick Panatrope has loud 60 cycle hum

Brunswick Panatrope has loud 60 cycle hum - Printable Version

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Brunswick Panatrope has loud 60 cycle hum - marcapra - 08-09-2010

I just got my 1926 Brunswick Panatrope back from the shop. It is a phonograph only model P-9 with a chassis that was made by RCA and looks like a RCA Model 104 speaker, sometimes called a Tomcat. It works now, but has a loud 60 cycle hum. I guess it could be a bad transformer? any ideas of how to fix it? Marc.

Re: Brunswick Panatrope has loud 60 cycle hum - rghines1 - 08-10-2010

A bad transformer seems unlikely. Would suspect the power supply first for high ripple or AC. Should be easy to check with a meter. Think these older RCA power supplies used large paper caps that become open and are in a potted metal box which make rebuilding them an awful job.

Other possiblility I can think of is the shielding of the cable from the pickup unit. See if it has a shielded wire that has become loose or broken. Richard

http://www.nostalgiaair.org/Resources/517/M0039517.htm

Re: Brunswick Panatrope has loud 60 cycle hum - Texasrocker - 08-15-2010

If the power supply caps are hard to get to, as with many of these older sets (some even buried in tar in the power supply section), could be the shop that did your repairs didnt replace them? If they did replace them, perhaps those caps are visible now? If so, you can jumper-in ( in parallel) across the filter supply caps with ones with abit higher UF rating, observing polarity with schematic, to help rid excess 60 cycle hum. Its trial & error test using added capacitors across what already is in place in the power supply. Most older sets use lower uf ratings with higher voltage ratings, and it can be dangerous jumping in added caps. High voltages are present in the power supply, so be VERY careful and let your orig caps discharge for several minutes before jumpering in any added uf rated caps. Never exceed more than minimal uf's needed to rid the hum because doing so can raise B+ voltages abit also, usually not that critical tho. For example, if the schematic calls for a 10 uf @ 450 volts, and you still have hum, try jumpering in with a set test wires with insulated alligator-clips on each ends,add another 10uf @ 450 volt cap in parallel with the orig cap already in place, observing positive & neg polarities on the caps. Many times you can hear the hum disappear instantly once the added uf's are connected.