|
|
|
#1
08-09-2021, 11:07 PM
|
|||
|
|||
|
Noisy 9V Batteries?! & An odd issue with an RCA 5T Radio
Hello everyone tonight I was listing to my 1937 Coronado 630B Battery Powered Farm Radio and I was trying to tune in some stations and all of the sudden starting around 900 kHz on the dial and going down I heard a terrible buzzing noise (assumed electromagnetic interference) and it got worse the lower on the dial I tuned.
The weird thing is that the buzzing noise would go away as soon as I took my hand away from the radio, and so something I did was I waved my hands over the whole radio until I got by my 90v "B" Battery pack (10 9V batteries daisychained together) and when I touched the "B" battery pack the radio buzzed so loudly that the radio was not able to pick up anything but EMI Buzzing but then when I moved my hands away the buzzing cleared up and the radio came in fine. I thought that the whole point of a battery set was that it wouldn't pick up EMI as easily or other AC line noise? Anyways, has anyone ever heard of 9V batteries that emitted EMI when touched? I certainly haven't, sounds to me like defective batteries...  Any ideas anyone? Also as a side note I have an RCA 5T AM/SW radio that I recently finished restoring electrically and that radio picks up stations quite well on both AM and Shortwave during both day and night, but something I've noticed recently is that between 540 and 1300 kHz on the dial I hear a loud buzzing noise similar to the noise I just talked about that my Coronado radio making except that the RCA 5T does it all the time regardless of whether or not I'm touching the receiver or not. The noise oddly enough is affect by when my house's AC unit kicks on and off (when the AC unit kicks on it make a popping noise on the radio and the volume cuts down by almost half of what it was playing at previously and the buzzing noise goes away, but then when the AC kicks off the radio goes back to full volume and the buzzing noise returns so I'm not sure what's going on there. Its acting almost like an AVC issue but the AVC should't be affected by the simple act of an AC unit kicking on should it? Any help with these issues would be appreciated. Thanks. 
|
|
#2
08-10-2021, 11:08 AM
|
||||
|
||||
|
Random thoughts:
Seems very peculiar that a battery could do that. Could it be some kind of regeneration? Does it only do it with your hand? How about if you place some metal (aluminum foil) near the radio? Does the set have an external ground and/or antenna? For the HVAC effects, how about snooping around with a transistor portable to see if you can locate the source? Edit: the source of the buzz could be completely separate from the HVAC, which may be adding its own effects somehow.
|
|
#3
08-10-2021, 12:55 PM
|
|||
|
|||
|
Quote:
The radio does have a ground wire lead but it's not hooked up because I don't have a good spot to hook it up to. As for the buzz on the batteries on the Coronado Radio I figured out it was my laptop power supply brick apparently was making noise which is weird because it didn't used to be that noisy... a failing laptop power supply?! My desktop computer's power supply does the same thing but 10x worse. As for the HVAC noise on the RCA radio, I know it's something with the HVAC because it only does it when the HVAC system kicks on and off (the popping noise and the audio raising and lowering volume) the buzzing I think was the same issue as the Coronado radio.
|
|
#4
08-10-2021, 01:24 PM
|
||||
|
||||
|
When an AC system turns on or off a relay opens and closes power to 2 big fan motors...When that happens the relay contacts spark and sparks generate pop noises on all radio frequencies.
Big loads like AC systems, electric clothes dryers and ovens can sag line voltage... measure line voltage with the AC system off and on and use a variac with AC off to simulate the line voltage with the AC on and if volume drops the same amount you'll know it's the radio being sensitive to line voltage... Sometimes when tubes get old they'll be strong at rated heater voltage but loose emission strangely fast as heater voltage is decreased below it's rating.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
|
|
#5
08-10-2021, 01:27 PM
|
|||
|
|||
|
Quote:
|
| Audiokarma |
|
#6
08-10-2021, 07:57 PM
|
|||
|
|||
|
Ok so a little update, I checked for "voltage sag" when my AC turns on and off and it actually does the opposite, the baseline voltage is 119.5 volts AC coming out of the wall when the AC is not running and spikes to between 120.5-121.1 Volts AC coming out of the Wall when the AC is running... Is that normal?!
 I don't know if this would affect things or not but the way whoever put the AC in in this house did it, they wired the AC Compressor up to an old ungrounded 220V Electric dryer outlet that was in the old laundry room in the basement of my house, and my house was built around 1933 and none of the outlets in my house are actually grounded (they have grounded outlets installed but they aren't actually grounded because the house still has its original ungrounded romex wiring running throughout the house yet). I hope this is enough information to go by to figure out what's going on with my radio.
|
|
#7
08-10-2021, 09:54 PM
|
||||
|
||||
|
This voltage variation sounds like it's a trivial change in the waveform, which the meter picks up, not a change in the fundamental power.
Do any other radios behave the same way?
|
|
#8
08-10-2021, 10:26 PM
|
|||
|
|||
|
Quote:
I have a mostly functioning Zenith J733 AM/FM Clock Radio from 1952 that does some bizzare stuff every once in a while, but it doesn't have AVC built in, which might be part of the reason why it functions/acts the way it does. Like I said my Coronado farm radio does some funky stuff but its only affected by "radiated" RF noise rather than AC Line noise since its a battery set. I also have a 1967 vintage Magnavox AM/FM/FM AFC dual speaker radio that also seems to be affected by oddball AC Line Noise and that set was completely recapped (also it was supposed to have one of those line coupled FM antennas but it was missing so i had to juryrig one up for it but it doesn't seem to work quite right still. Other than those issues I really don't have much trouble with my radios.
|
|
#9
08-11-2021, 12:13 AM
|
||||
|
||||
|
? A 1952 model that doesn't have AVC? Are you sure?
|
|
#10
08-11-2021, 02:36 AM
|
|||
|
|||
|
Quote:
|
| Audiokarma |
|
#11
08-11-2021, 10:12 AM
|
||||
|
||||
|
Oh, OK - happens to all of us.
|
|
#12
08-13-2021, 11:58 AM
|
|||
|
|||
|
OK, so oddly enough the RCA 5T's issues suddenly cleared up last night and was coming in relatively noise free and really loud last night and even the shortwave band was coming in loud and clear last night.
Same for the Coronado, its really weird it's now suddenly coming in just fine. I wonder if it wasn't because of all of those storms that rolled through the past couple of nights...
|
 |
|
|
Linear Mode
