[Mike L]

Not sure why but my model 84 has recently developed a hum in the audio. It is present all of the time and stays the same in that it does not get louder with volume. At first I thought it was interference hum on the A/C line, but I plugged my model 80 in the same outlet with no issues. I also swapped out tubes in the 84 one at a time but no help. Paralleled a new electrolytic cap on the 8 mfd section and then the 4 mfd section with no change. All caps were replaced and it was working great until just recently. Also no difference if it is just turned on (cold) or on for an hour. Any ideas?

[morzh]

Could it be mechanical hum ftom the power transformer? Have you verified the sound comes from the speaker?

[Mike L]

Yes it is defiantly from the speaker. The radio is also still out of the cabinet.

[morzh]

See if any wires touch or disconnected. If it developed it while still on the table this could be a contact issue. Turn it on its side, wiggle wires, etc.

[Radioroslyn]

> my model 84 has recently developed a hum in the audio.
Merry Christmas!!!  Have you been good this year???

Kidding aside check your chassis or good ground connections. A rivet over by the 42 socket comes to mind. For grins try grounding the grid cap on the second 77 tube to hear if the kills the hum.

[Mike L]

I did recently replace all three speaker wires as they were in bad shape. Maybe I have a bad solder joint. I'll check the other suggestions as well.

[tbone]

I did recently replace all three speaker wires as they were in bad shape. Maybe I have a bad solder joint. I'll check the other suggestions as well.

I recently restored one and the hum was not power supply related. The 77 2nd detector shield and tube socket had poor ground to the chassis. By design this radios audio section runs wide open and is susceptible to hum.

The only fix is to clean the shield and mating socket, and top cap with a scotch brite pad for a good ground. Then you need to drill out the socket rivets, clean the area, and use good screws with star washers.

When I was done, the radio was completely quiet. Good luck and Merry Christmas.

Tony

[Mike L]

I think my issue is actually ground loop hum. Can it be the some radios are more sensitive than others? Strange the older Philco 80 was not effected. I turned on my old Aircastle today and there was an annoying interference hum and buzz. Turns out it was a small electric space heater in the basement. Every time it kicked on this would happen. Also I have "can" ceiling lights on a dimmer that cause this problem too. Is there a circuit design for a strip terminal type that I can make to plug all my finished radios in, to enjoy in the living room? Humm eliminators are $70 a pop. There cant be much to them to make your own.

[morzh]

If it is across the band and does not get louder with volume it is not likely the interference.
As said, check the GND rivets etc. If it popped from nowhere....

OK, have you try to GND the input of the audio tube and see if it goes away? You need to try to trace it.

[Mike L]

This is happening on several radios. Radio is playing, wife turns on the light in the kitchen (not fluorescent) and there is a loud hum and buzz. Turn it off and its gone. Same with a space heater in the basement, radio on the first floor. Kicks on and hum and buzz. Turns off and gone. Seems no matter what outlet I use same result.

[morzh]

Well...if THIS radio behaves exactly the same as some others (I don't then understand why you say "recently developed" - maybe you didn't notice it before) - than the problem is solved and we can move to other subjects?

[Ron Ramirez]

I think what Mike is trying to say is that the problem clearly is not with your radio - it is with a light in your kitchen.

Does the light fixture have CFL bulbs? If so...there's your answer. Replacement will cure the trouble.

Does the light fixture have LED bulbs? If so...they must be the cheapest of the cheap and need to be replaced. My house is nearly completely converted to LEDs and I do not have such troubles.

Another thought: Check that kitchen light fixture, or have it checked by a competent electrician. If it has incandescent bulbs or good LEDs, then there may be a problem with the fixture itself, the wiring at the fixture and/or the switch and/or wiring connected to it. Don't put this off - you may have a serious electrical problem that could result in a house fire.

I can see how a space heater could generate hash that interferes with AM reception. The answer is obvious - turn the space heater off while listening.

(do you know how hard it is to type with a cat between you and the keyboard?)

[Mike L]

I guess at this point what I'm asking is, that if the hum is being introduced through the AC line from other electrical items in the area not necessarily on the same electrical circuit is there something that can be done to help eliminate that as a source? Isolation transformer with a power strip?

[Mike L]

"(do you know how hard it is to type with a cat between you and the keyboard?)"

All too well


"Another thought: Check that kitchen light fixture, or have it checked by a competent electrician. If it has incandescent bulbs or good LEDs, then there may be a problem with the fixture itself, the wiring at the fixture and/or the switch and/or wiring connected to it. Don't put this off - you may have a serious electrical problem that could result in a house fire."


All lights are incandescent but are on dimmer controls. Everything passed inspection when the remodel was done.

[Ron Ramirez]

Well, there's your answer...the dimmers. Many if not all modern dimmers are notorious for producing RFI.