I know this has probably been asked more than once, but what causes background buzzing on old AM tube radios?
I'm not talking about hum, as when you tune in a station this buzzing goes away and the station comes in clear with no buzz or hum.
It seems louder on some radios than others, and also often gets louder on one end of the band than the other.
Completely restored radios also do it, so it's not the old parts.
Just wondering what this is, and if there's a simple general way to reduce it.

Frank,
Chances are that if the radio has been put in reasonable working order, then what you hear is "pollution" of the airwaves. Way back when radio first got going the number one pollutant was static: static from the atmosphere, thunderstorms, etc. As things progressed and power lines spread across the country, things got worse with the noise from electric motors, elevators, trolleys, the powerlines themselves...anything electric putting out "static". These old radios receive all that stuff so easily because they are designed to receive A.M. and all the junk out there is a form of AM. That's why FM became all the rage. Your radios will typically pick up more of it on the upper end of the dial because that's where they are more sensitive. A really good radio, one with an RF amplifier and well adjusted typically picks up very well all across the band: all the weak stations...and lots of "static". And when you tune into a strong station, the noise seems to go away, simply because the station is stronger than the noise. Use an outside antenna and you give the "real" radio signals a better chance of "getting" to your radio to overpower the noise. Strictly speaking, the pollution is not all static, especially these days. Today we are plagued with the pollution coming out of computers, video monitors, cable TV, the TV itself, the CD player, satellite receiver, coffee maker, cell phone charger light dimmers, touch lamps, energy efficient bulbs....the list is endless....all making weird buzzes, chirps, and squeals. Much of the stuff is modulated such that it sounds like some sort of static. And almost all of this stuff pollutes even if it is turned off! You have to actually pull the plug out of the wall. My expensive DVD player only gets plugged in when someone is watching a video.
That's the bad news. The good news is that a good bit of airwaves trash can be minimized if you take the time to unplug stuff around your house and learn to hear what the solid state little devils sound like. The task is tougher when you live "close in" with your neighbors, or your radio is in the same room with the offending device. Generally the most offending stuff doesn't get far, and you typically find your own dwelling to be the worst offender, but stuff does get to the set from outside. Still, one of the best treatments is a good outside antenna.
The hunt for airwave pollution can be both frustrating and fun. It took me two months to find out that the big, loud signal parked right next to my favorite local AM station at 1400kHz was the charger for my cellular phone. I chucked it rather than put up with the squeal.
Hope this helps.
Anyone want to list their "favorite" radio "trash" generator?
Jim

Frank,
Probably flourescent lights, a variety of dimmers or even PC's/hardware like wireless. The gain (AVC) is wide open between stations, but when tuned to a stronger station, the AVC takes over, reducing the gain, eliminating the low level background buzz.

marv

:I know this has probably been asked more than once, but what causes background buzzing on old AM tube radios?
:I'm not talking about hum, as when you tune in a station this buzzing goes away and the station comes in clear with no buzz or hum.
:It seems louder on some radios than others, and also often gets louder on one end of the band than the other.
:Completely restored radios also do it, so it's not the old parts.
:Just wondering what this is, and if there's a simple general way to reduce it.

Thanks for the quick response, that explains it.
Plus we have so many devices plugged in here in every room, chargers, CD/DVD players, etc., and rheostats on many of the incandescent bulb fixtures, as well as a bunch of fluorescent lights as well. In addition to that, a wireless internet system.
One wall switch on the same circuit where I plugged in a just-fixed radio (to show my wife) has a rheostat and when I turned on the light, the buzzing got 5 times worse.
On the other hand, as you say, the antenna does help. I didn't use an outside antenna, but just by rotating the radio so that a weaker-to-middling station came in better, it rejected the buzz previously heard on that station as well. Thanks...

:Thanks for the quick response, that explains it.
:Plus we have so many devices plugged in here in every room, chargers, CD/DVD players, etc., and rheostats on many of the incandescent bulb fixtures, as well as a bunch of fluorescent lights as well. In addition to that, a wireless internet system.
:One wall switch on the same circuit where I plugged in a just-fixed radio (to show my wife) has a rheostat and when I turned on the light, the buzzing got 5 times worse.
:On the other hand, as you say, the antenna does help. I didn't use an outside antenna, but just by rotating the radio so that a weaker-to-middling station came in better, it rejected the buzz previously heard on that station as well. Thanks...

Don't forget, anything with a microprosser is a noise generator and a half. My sattelite receiver will cover up local stations fifty feet away. If you're talking buzz only, you are probably hearing sixty or one hundred twenty hertz from the power line, probobly a dimmer or flourescent light.

Lewis L.