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24th Sep 2013, 10:35 pm
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#21 |
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Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: Murphy A372
It does sound as if it may be interference, some sets are more prone than others, however, shorting the aerial does damp the aerial coil reducing the impedance on the grid so its by no means conclusive.
When you switch off, a radio normally continues to work for a few seconds. Does the noise fade with the radio or disappear immediately? |
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24th Sep 2013, 11:09 pm
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#22 |
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Octode
Join Date: Jul 2005
Location: Newport, Gwent, UK.
Posts: 1,623
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Re: Murphy A372
Hello,
I am going to compare the set with another valve radio to see if the noise comes at the same frequencies in both. Then I will check about whether it fades away on switching off. I did think it was a faulty 10C1 valve but it seems instead as if the fault, if any, might be in the aerial circuits. Even when tuned to a strong station (on AM) there is a slight background 'hash' noise present. Michael |
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25th Sep 2013, 9:59 pm
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#23 |
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Octode
Join Date: Jul 2005
Location: Newport, Gwent, UK.
Posts: 1,623
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Re: Murphy A372
Hello,
Well I have now tested this radio against another valve radio (after I found one that was actually working ... Pye Fenman II). There is definitely something going on on the LW band (and possibly MW - VHF is fine). The 'noise' is there whereas on the Pye it is not. When switching the set off, the noise disappears (fades) to be replaced by ordinary hum in the very short time it takes to switch off completely. Could all this be caused by a faulty local oscillator/mixer valve (10C1)? Michael |
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