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22nd Oct 2019, 2:42 pm
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#1 |
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Octode
Join Date: Jun 2005
Location: Sheffield, South Yorkshire, UK.
Posts: 1,227
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Buzz on VHF
My Bush VHF 72 works well except there is a buzz/hum on stations only on VHF .What are likely causes? It has had a minimal overhaul by me.
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22nd Oct 2019, 3:19 pm
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#2 |
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Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
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Re: Buzz on VHF
Heater-cathode leakage in the VHF front end valve? Missing or low value mains filter capacitor, leading to modulation hum from the rectifier?
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22nd Oct 2019, 3:35 pm
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#3 |
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Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,431
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Re: Buzz on VHF
A couple of more thoughts.
Heater cathode leak in the UABC80 and C41 O/C, maker manual reference.
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Frank |
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22nd Oct 2019, 5:43 pm
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#4 |
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Hexode
Join Date: Jan 2018
Location: Cannock, Staffordshire, UK.
Posts: 268
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Re: Buzz on VHF
I would also suspect C41 (maker service sheet) or if the phantom fiddler has been inside before you got it it could be out of alignment - does ift4 look like it's been twiddled?
Is it a harsh or smooth sounding hum? And If you are really close to the transmitter or they are using high modulation that can cause strange sound effects. Is it the sane ob all stations? Derek |
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