I have this radio
which has been modified to take the audio signal from the input to the volume control.
My desire is to feed this radio into a solid state MPX decoder and drive a small T amp along with a pair of vintage Automatic Radio speakers.
The problem is I am pretty sure this radio has a de-emphasis circuit. I fed it into my Ampex 520 MPX decoder and got muffled highs. I will need the schematic to see if it has a de-emphasis circuit and then remove it.
All will be powered by a 12 volt rechargeable battery with a 9 volt regulator circuit for the radio. I will need to build a charging circuit for the battery though. I plan on possibly using an external 12 volt power supply and will need to make a circuit that will switch the battery to a charging circuit and still allow the radio to play whenever the unit is connected to the 12 volt power supply. I assume I can just use a resistor in series with the battery to allow the recommended charging current to the battery, but I will need an automatic switching circuit though which could be done via a diode in series with the power supply and circuit so that only the power supply will turn on the relay and switch the battery to the resistor. That would reduce the available voltage to the circuit by .7 volts or less while battery is charging, but that should be ok. I could always use a 16 volt battery and a 12 volt high current regulator circuit along with a 16 volt power supply. That way I would have 12 volts regulated and the radio could play longer between battery charges. I have no clue how much current a T amp would draw though. I suppose I would only need around 10 WPC as that is about what the speakers I have can handle.
Should be an interesting creation when I am done. Best part of this is I can even feed the AM audio signal through the MPX decoder and while not stereo it will play in both speakers.