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Old 13th Nov 2015, 11:17 pm   #1
Nightcruiser
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Default 1931 Marconiphone 42 oscillating problem

Listening to the old marconiphone 42 this week the set suddenly lost all signals on MW/LW from the powerful sound it had. Neither is there any life or improvement from the aerial socket when probed.

It will still oscillate on both of the wavelengths but can no longer bring in the stations.

I've cleaned all the valve pins thoroughly of the MS4B and MH4 etc and given the sockets a clean at the same time but no joy.

Has anyone any ideas please

John
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Old 14th Nov 2015, 12:29 am   #2
Skywave
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Arrow Re: 1931 Marconiphone 42 oscillating problem

Sounds like R.F. instability to me. Given the fault conditions (i.e. not wavelength specific), the I.F. amplifier stage is a strong contender. Have a look inside and see if you can see any 'waxy' capacitors. If there are any, change them. Ditto any capacitors bearing the name 'Hunts'.

Al.
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Old 14th Nov 2015, 12:42 am   #3
TonyDuell
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Default Re: 1931 Marconiphone 42 oscillating problem

Err, what IF amplifier stage?

According to the Trader Sheet this is a TRF receiver with a regenerative detector. I assume the 'oscillation' refered to means the detector valve (MH4) can be got to oscillate by turning up the reaction control.

I would therefore start by checking round the RF amplifier, the MS4B. Make sure the heater is not open-circuit, then measure the anode voltage (on the top cap of this valve) and the screen grid voltage.

An old trick is to couple an aerial to the top cap (anode) of the RF amplifier through a small capacitor (to prevent HT+ ending up on the aerial) and see if you can receive a local (strong) station. If you do this, do not let the set oscillate as it will act as a transmitter....
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Old 14th Nov 2015, 2:24 am   #4
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Default Re: 1931 Marconiphone 42 oscillating problem

Thanks guys

The MS4B seems now to be the culprit so im gonna have to source another excellent one from somewhere to keep me fired up on these forthcoming chilly nights

John
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Old 14th Nov 2015, 10:26 am   #5
jonnybear
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Default Re: 1931 Marconiphone 42 oscillating problem

This any good shows as equivalent (NVM).http://www.ebay.co.uk/itm/New-Old-St...AAAOSwkZhWRHG4.
John
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Old 15th Nov 2015, 2:41 pm   #6
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Default Re: 1931 Marconiphone 42 oscillating problem

Thank you for the info John - I shall take a look.��
the only problem i often find with ebay valves is sometimes its a duff valve that was put back into the new valves box when a replacement was necessary.. An old habit often used by the on site repairmen over the years but as lng as it keeps me going .....����

John

Last edited by Nightcruiser; 15th Nov 2015 at 2:47 pm.
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