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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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14th Jul 2019, 10:56 pm | #1 |
Retired Dormant Member
Join Date: Jul 2019
Location: Kaunas, Lithuania
Posts: 1
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FRG-7 Quiet hum
Hi folks!
I had some troubles with my Yaesu FRG-7. One day it went silent. Found & fixed the problem - it was faulty rectifier diode. While dealing with this issue, I've noticed quiet hum from speaker (when volume is at 0%, or antenna is disconnected). Maybe it was before - just didn't paid attention to it. It's more noticeable while using headphones or trying to record something with a laptop. I've replaced capacitors. Not all (yet), but majority of them. Few difficult to access - left. But most essential ones (power supply) - replaced. In everyday use - listening shortwave broadcast stations & hams with speaker - it's almost / completely unnoticeable. But using headphones at low volume levels (<5-10%) humming it's a bit annoying. I've recorded that hum. Looked at spectrum - it's mostly 50 Hz tone (mains frequency in my country, I'm from Europe). So... it's normal for 1970s low / mid-range shortwave receiver, or it's something else? Or it's OK and I'm way overthinking this issue? |
18th Jul 2019, 6:13 pm | #2 |
Heptode
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 690
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Re: FRG-7 Quiet hum
Hi Antony,
I have an FRG7 and have never noticed a hum. I almost always use it on the loudspeaker though so it maybe only a problem on headphones. I guess one option would be to use lower sensitivity headphones or load the existing ones with a resistor. You would then need to increase the audio gain but the hum level should be reduced.
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Keith Yates - G3XGW VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm |
19th Jul 2019, 10:55 am | #3 |
Hexode
Join Date: Jul 2006
Location: Sheffield, South Yorkshire, UK.
Posts: 312
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Re: FRG-7 Quiet hum
The power supply has a full-wave rectifier (D408 and D409) so any ripple should be at a frequency of 100Hz. So maybe you still have a bad diode?
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Always expect the unexpected... |
19th Jul 2019, 11:59 am | #4 |
Heptode
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 690
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Re: FRG-7 Quiet hum
As it's at such a low level, it's probably just capacitive pick-up by the audio stages from the mains wiring within the receiver.
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Keith Yates - G3XGW VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm |
20th Jul 2019, 4:03 pm | #5 |
Heptode
Join Date: Jan 2008
Location: Birchington Kent, UK.
Posts: 595
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Re: FRG-7 Quiet hum
Had this problem with two Kenwood R5000 receivers.
The cause was poor eathing on the IF / audio output pwb. Resolution was by applying Deoxit to the earth return / mounting tabs.
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Regards Pete |
20th Jul 2019, 5:36 pm | #6 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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Re: FRG-7 Quiet hum
It might also be worth following the low level AF wiring.
It will almost certainly be in screened cable but it wouldn't be a first time to see it routed half a turn around the mains transformer with only small spacing. Pye managed it in one transmitter. |
22nd Jul 2019, 12:02 pm | #7 |
Triode
Join Date: Dec 2015
Location: Les Salles Lavauguyon, France
Posts: 43
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Re: FRG-7 Quiet hum
But here's another idle thought, the FRG-7, which is not exactly a Hi-Fi receiver, would have been "specified" with the Yaesu headphones designed for comms audio or a very ordinary 2" ~ 4" loudspeaker. Neither have any real response below 200Hz, but your everyday headphones designed for music and centre of the head thumping bass most certainly do. . . . . . . .
I doubt Yaesu cared too much about an ultimate low hum level. . . . . . R. |