[patrician56]

Hi,
I have a Fisher Custom Electra (mono) with the K15 chassis (1956). I have enjoyed this for the last 15 years.  During my ownership I have had capacitors and resistors replaced to the point that "we got 'em all". I use this instrument primarily for playing my 78s and older mono LPs and 45s (Garrard RC 88/4 changer with a GE VR cartridge).
I wanted to listen to a local FM broadcast on the radio and noticed that there is a "hum" that occurs between about 90 and 94 on the FM band. The station that I wanted to listen to was at 92 and the hum was annoying. If I go below 90 on the dial it disappears as well as above 94. No hum on either the AM or the phono. The volume of the hum increased as I advance the AFC control knob. I was using the factory dipole antenna and switched to the roof antenna connected by coax. This made no difference.
I'm at a loss as to the origin of the hum and I was wondering if anyone might have any thoughts as to what might be causing it. btw, no light dimmers, computers or any other electronics within 30 feet of the receiver when it was operating.
Appreciate any suggestions.
Fran

[TV MAN]

Have you "upgraded" anywhere with LED bulbs around the house? Or, your power company "upgraded" your meter or something? I have had fits with these new bulbs, and even if they are far away, if they are on the same circuit, they could cause problems. We have a buzz that comes and goes on AM, and I have yet to find the source. Even opening our refrigerator door causes a buzz. I have had instances where those LED bulbs will kill a RF signal - try screwing those bulbs into a garage door opener and see what happens? Anyway - food for thought.

[patrician56]

Hi Tim P.
Oh yes, I am aware of the "gremlins" released with LED bulbs so when this issue became evident I did a search and turned off any that were on...No change.
I just though of something. I replaced the indicator bulbs (AM, FM, Phono etc.) with new LED bulbs.....I wonder if that might be the issue?
Thanks,
Fran

[rfeenstra]

anything with a switching supply can cause noise.  I've "de-buzzed" a lot of LED lights and dimmers by putting a choke in the AC line. I think an LED in a piece of electronic equipment won't buzz unless the it is supplied with a switching supply or a DC to DC converter.  I had a couple of momentray buzzes every few seconds that turned out to be battery chargers for my various battery powered tools.  Very annoying.

[Ron Ramirez]

I replaced the indicator bulbs (AM, FM, Phono etc.) with new LED bulbs.....I wonder if that might be the issue?

I doubt it. I've been replacing dial lamps with LEDs in nearly every Fisher that I own, along with some of my Philco sets. They have not caused any humming or interference at all.

What sort of antenna are you using? I have experienced interference at times just by walking past an operating FM radio, or standing in a certain spot in the basement, due to poor antenna placement. Moving the antenna usually cures that. If your Custom Electra is operating on a built-in antenna, an external FM antenna might help.

[patrician56]

Hi Ron,
I have both the factory Dipole antenna and an FM antenna in the attic attached to a rotor and fed via coax. There was no improvement with the hum (sounds like 60 cycle hum, not too loud, but annoying) using the attic antenna. I am considering moving the console (ugh!) across the house to another room to see if there is improvement. There might be interference from something in the house next door, or something in my house that I overlooked......
Thanks for the thoughts.
BTW, I did bring a portable radio into the room and there was no hum from that in the FM band between 90 and 94 on the dial.

[Radioroslyn]

I'd just for grins try plugging it in to a long extension cord and plug that into an outlet in a different room in the house. If you have a really long cord you can try rolling it up to make a rf choke. Maybe there's a clue with giving this a try.

GL

[patrician56]

Terry,
Well I tried the extension cord route - plugged the Fisher into a 75' cord coiled in an 18" coil; plugged into a 50' extension cord and plugged that extension cord into a receptacle several rooms away. Turned on the radio and 90% of the hum has disappeared. Only a faint hum just at 92 meg on the dial....I guess I have noisy circuits in the listening room.... Any recommendations on a more permanent filter solution?
I thank you very much!
Fran

[Radioroslyn]

>Any recommendations on a more permanent filter solution?

I'm glad you asked that... [Image: http://philcoradio.com/phorum/images/smi...on_lol.gif]
A couple of things come to mind. On some of the older FM sets the fm ant is connected the ac line thru a small value cap. At rf frequencies this cap looks like a short and couples all the noise that's on the line into the rf amp stage. So if your set has this configuration removing that cap would help.
More of an experimenter than a break out the slide rule and calculate kind of guy. If that being said I think something that looks like this may be  helpful:    
In terms of turns would start with about 5 and perhaps up to 20 choosing the number that give the best attenuation. You can also try connecting a wire from chassis ground to earth ground. This is made simple if you have hot water baseboard heat. You can just clip the ground ware on the one of the heater fins. Using the 3rd wire on the outlet isn't a good idea as you'll probably find more noise there. I'm sure there's someone smarter than I that has some better ideas.

GL

[patrician56]

Terry,
Thanks for the schematic for the "experiment"! I will pull together what I don't have and hopefully will have a reportable result within a week. I have as yet to try the chassis ground to earth ground, but the room that the Fisher is in has cast iron baseboard type radiators all around the room, so that should be easy.
Thanks again,
Fran