Buzz or hum on station only - Printable Version

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+--- Thread: Buzz or hum on station only (/showthread.php?tid=18353)

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Buzz or hum on station only - epdowd - 05-03-2018

Hello, I'm a new guy here and have a question with my Philco farm radio Model 42-122.
I get a hum maybe buzz On Station Only. Now to explain : I do not have that problem when I run it on batteries.
I have the problem when I use the 90vdc - 1.5vdc power supply I made. I followed a well used version of the power supply - battery eliminator. I've checked everything for proper hook up. It seems as if it is the power supply at fault, I would get the hum all across the band, station or not. I do get the station fairly clear but with the noise riding it,, only on a received station. Thank you for any help, tips.

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RE: Buzz or hum on station only - Arran - 05-04-2018

Hi;
  There is a 10 uf cap between the B+ and the chassis, which is also connected to A-, this is an electrolytic cap, and if it's dried out the set will hum whilst running it off of a power supply, I don't know if the same is true on batteries. It should be replaced anyhow because if it shorts out it could damage the tubes, it isn't likely but may happen. Use at least a 100 volt cap here as it has 80 vdc across it. If this isn't the issue then the power supply may have a fault, or may need a capacitor to filter the power line.
Regards
Arran

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RE: Buzz or hum on station only - morzh - 05-04-2018

If your power supply is of the switching type, it can, even if producing clean voltages, radiate EMI. When you made it, have you followed standard anti-EMI practices? One way of remedying this would be putting the power supply in a metal grounded box (grounded from outlet PE), and put a ferrite bead (make several turns) around the cable, as close as possible to the box.
This is, of course, if your voltages out of the power supply are clean.

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RE: Buzz or hum on station only - epdowd - 05-09-2018

Thank you for your replies. I'm slow on answering back but I haven't had a chance to work on the power supply. I will shortly and let you know what I come up with.  Thanks again..

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RE: Buzz or hum on station only - epdowd - 05-13-2018

I finally got back on this power supply. I've swapped everything out, still have a buzz. (turned off all the house circuits to double check, again) it's either the board or wiring.
It's such a simple circuit ,, two wires in fact. I'll take it apart and do it again. Maybe use different type board. This is the copper through hole board, may be some cross feed in the connections. Anyway I'll lay this thread at rest. Thanks.  

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RE: Buzz or hum on station only - morzh - 05-13-2018

It is had to understand and help without schematic or seeing what it is. If you could scan the sch and provide the photo of what you've done we could try to at least attempt something, else it's just guessing.
It is not a type of board, I could guarantee you.
Without understanding the possible reason you are destined to keep struggling.

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RE: Buzz or hum on station only - gregb - 05-13-2018

Have you tried attaching the A- to a good earth ground? That may help.

Gregb

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RE: Buzz or hum on station only - epdowd - 06-02-2018

OK, I'm back in town and fiddled with the radio some more, I kept blaming the power supply but wala !!, all it needed was Earth Ground as suggested  . What confused me more was the buzz was only on a station. I don't remember of ever having that problem before but my One brain cell doesn't work like it used to  .
Thank you all  . Harv.

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