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Old 15th Oct 2021, 2:56 pm   #1
Andrew_L
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Default Gramophone Input and Bluetooth

Hi,

I have done a search through existing articles and there are some articles related to this but I have not quite seen the answer (or have not understood it) - very much beginner end of things.

I got hold of a Etronic ETA539 to, at a minimum, try and understand antique radio and restoration (it was cheap). Am still doing research but if I can identify all the parts etc (I have got hold of a trader service sheet) I will probably have a go at replacing the caps etc. It does have a transformer coming off the mains so I believe it is not a live chassis (I am not going to plug it in till I work that out 100% and have and isolating transformer)

It has a input for a "gramaphone pickup". I have seen some stuff that implies a headphones out can be plugged straight in but with low signal (is this due to impedance matching issues that some comments reference). Is that correct? Would it be possible to modify this connection to add in a bluetooth receiver internally to the radio so it is not visible.

Please note that I have no clue if it will even work yet so the entire radio may be a dead loss but as I say it was cheap.

A
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Old 15th Oct 2021, 3:04 pm   #2
paulsherwin
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Default Re: Gramaphone Input and Bluetooth

The gram input was designed to work with a crystal record cartridge with an output of a volt or two. It will work with a modern line level mono source such as a CD or DVD player, or you can hook up a Bluetooth module. A headphone output can also be used, though the output may be a bit low, depending on the device.

You will need to sort out the radio before doing this though, especially if it's completely unrestored. Please bear in mind that there are high voltages inside valve radios, and while they're unlikely to kill a healthy person, they can give you an extremely unpleasant shock.
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Old 15th Oct 2021, 3:39 pm   #3
unitelex
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Default Re: Gramophone Input and Bluetooth

I echo Paul's comments and recommendation re: sorting the radio first.

Yes you can add Bluetooth to the "Gramophone pickup" input.
The Bluetooth can also be hidden internally, and is quite straightforward to get working however to make it work well, without hum and buzzing interference usually requires a little know how and attention to detail.
Happy to help and advise on this when you reach that point.
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Old 16th Oct 2021, 7:10 am   #4
Edward Huggins
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Default Re: Gramophone Input and Bluetooth

This 1949 set uses 7 series 6.3V heater valves, so is highly likely to have a mains-isolated chassis.
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Old 16th Oct 2021, 11:10 am   #5
sortedradio
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Default Re: Gramophone Input and Bluetooth

You may find this a useful thread regarding Bluetooth

https://www.vintage-radio.net/forum/...d.php?t=183586
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Old 16th Oct 2021, 11:49 am   #6
Gabe001
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Default Re: Gramophone Input and Bluetooth

From a quick look at the schematic it looks like it has a gram setting on the waveband switch, so no radio muting required. The hand-drawn circuit on the above mentioned thread should work well for you without any need to modify the krc-86b for radio muting. If you've replaced c12 (schematic on RM) you don't need an additional isolating capacitor on the krc-86b output.

As an aside, an external Bluetooth module works equally as well with much less hassle, but you obviously need to keep it charged.

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Old 16th Oct 2021, 12:44 pm   #7
Andrew_L
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Default Re: Gramophone Input and Bluetooth

Many thanks all for the advice and safety comments.

Yes the first task is trying to get it to work but I am also working on understanding the circuit at the same time so all a learning curve.

Cleaning and getting it out today.

A
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