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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 30th Mar 2018, 12:23 pm   #1
petergamston
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Join Date: Feb 2018
Location: Farnborough, Hampshire, UK.
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Default Gram input adaption.

I still don't have my Mullard 1764 (AKA Phillips 643A) working but, while I have the chassis out of the case I was wondering about adapting the 'Gram' input for some other source such as a modern DAB tuner or perhaps CD player deck.

I expect this has been covered before but as a complete newbee I'm quite clueless. My questions are :-

1) will the radio circuit have RIAA equalisation built in to this input and, if so how can I identify and bypass it - or is it better to connect 'downstream'.

2) would it be setup for something like high output mm cartridge outputs of about 1.7mV or would it 'expect' pre-amplification? Do I therefore need to attenuate (if that's the right word) an input from say a CD player and, if so, is it as simple as a resistor in series.

3) Out of curiosity is this frowned upon by the cognoscenti?

Thanks
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Old 30th Mar 2018, 4:21 pm   #2
TonyDuell
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Default Re: Gram input adaption.

Almost certainly the pickup input on this radio is designed for a crystal cartridge. So there would be no equalisation and the signal level will be a few hundred mV. It will not have been designed for a moving magnet cartridge.

People would play the line-level output of a tape recorder into the pickup input of a radio (particularly if the radio had a larger cabinet/speaker than the tape recorder) with no problems. I don't think it will do any damage to try feeding the output of a DAB tuner or CD player into that input, the worst that will happen if the signal is far too strong will be distortion. My guess is that it will be fine.
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Old 30th Mar 2018, 5:46 pm   #3
Kala_12
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Default Re: Gram input adaption.

If you are worried, why not just feed the output of the DAB tuner or CD player into that input via a simple potentiometer?
Stuart.
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Old 30th Mar 2018, 6:05 pm   #4
petergamston
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Default Re: Gram input adaption.

That's a good idea I hadn't thought of. Wasn't so much worried as ignorant - had wrongly assumed RIAA eq. would be an issue. Thanks to you and Tony.
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Old 30th Mar 2018, 6:11 pm   #5
ThePillenwerfer
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Default Re: Gram input adaption.

The vast majority of things I've stuck up a Gram socket have worked perfectly. A very few things have too low an output and need some sort of pre-amp.

As DAB radios &c usually have volume controls you can set that to what works best.

I can't speak for anybody else but it certainly isn't frowned on by me and I do it a lot. If fact it's the only use I have for radios without VHF.
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Old 30th Mar 2018, 8:26 pm   #6
John10b
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Default Re: Gram input adaption.

Take a look at the thread “...playing iPod through a Hacker Radio...”.
You just might find it interesting.
Cheers
John
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