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Old 19th Apr 2018, 12:36 pm   #1
Diniz Diniz
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Default Philips 470A pick up problem?

Hello everyone,

I just finished the repairment of a philips 470A. I'm doing it for free for a friend.

The set runs well in receiving mode. It has a selector to brodcast, short wave and long wave. I dont believe it has a PU position.

The set has a great (loud) sound, and even without aerial it is possible to tune some local AM station.
But when i connect a mobile phone in the PU, the sound is very low in all selector positions.

Is this normal, or is there anyway to proceed in this cases?

Thanks in advance.

(Apologies for the english writting)

Diniz, from PORTUGAL
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Old 19th Apr 2018, 1:11 pm   #2
'LIVEWIRE?'
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Default Re: Philips 470A pick up problem?

The pickup inputs on vintage radios are normally designed for High Impedance sources, i.e. the Crystal Pickups fitted to most record players back in the 1950s & 60s, so the most likely cause is an impedance/sensitivity mismatch. Mobile phones, and most other modern devices such as Ipods, CD Players, etc. have low-impedance outputs, so some form of pre-amplifier will be needed between the 'phone and radio. If the 470 has no P.U. positon, does in have a dedicated P.U. ('Gram) input? By the Way your English is way better than my non-existent Portuguese!
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Old 19th Apr 2018, 3:52 pm   #3
Diniz Diniz
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Default Re: Philips 470A pick up problem?

Livewire, I really appreciate your comment

I will try to find in the internet some way of a pre-amp between the phone and the radio. Do you ever deal with this problem??

I believe there is no position for PU (but I will check it, when at home), but it has a dedicated PU gram (see attached image from radiomuseum).

Thanks once more.
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Old 19th Apr 2018, 4:48 pm   #4
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Default Re: Philips 470A pick up problem?

According to the Trader Sheet for this set, there is a pickup socket, but no special switch position to use it. It is always connected to the volume control/grid circuit of the output valve.

It's only a single-stage audio amplifier (the output valve, no triode before it) so you will need a fairly strong audio signal to feed into the pickup sockets. I suspect it was designed for a high-output crystal cartridge.
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Old 5th May 2018, 7:12 pm   #5
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Default Re: Philips 470A pick up problem?

You cannot expect to much output from the pickup socket on this model as it is what is commonly known as a "Short Superhet", i.e. The audio amplifier consist of just a single Pentode valve - 'PEN4DD' in (British) home market models, or 'EBL 1' in export models.

So you would need some sort of external pre-amplifier between your 'Mobile Phone' and the Pickup Sockets. Or if it is badly matching input/output Impedances, you might need a low to high Impedance matching Transformer.
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Old 5th May 2018, 7:45 pm   #6
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Default Re: Philips 470A pick up problem?

You could try using an output transformer robbed from any nothing-special, Far East-made transistor radio (one from a valve radio would have too much step-up action) "in reverse" -- i.e., with the signal applied to the speaker winding and the connection to the PU inputs from the two ends of what used to have been the primary winding. If that is then overloading the input, you can try between the centre tap and one end.

If the transformer works fine except for excessive mains hum, try reversing the connections to the radio. You will get less hum when the outermost end of the winding is connected to the chassis, so the outermost layer of turns acts as a shield around the signal.
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