[Tiddat33]

Trying to figure out where to add the switching AUX jack and still use the radio volume control for the input.  I was thinking I could lift the left side of #63 and insert my switching AUX jack between #63 and #60….. 
Normally I would add it right at the volume control but this circuit seems different…. What am I missing??
Thanks!!!

[MrFixr55]

Hi Tidatt,


Definitely add to the volume control. The only difference is that this volume has a "Loudness Contour" tap. Break the connection to Cap 52 at the junction of Cap 50 and Resistor 51. The end of cap 2 goes to the common connector on the switch, the phone jack goes to one leg and a wire from the junction of C50 and R51 goes to the other leg. This thing should kick butt with an aux input. This appears to be a Class AB2 or Class B Audio system with the 42s triode connected. RCA did this also on their sets of this period.

[RodB]

I did this on my 650X and it kinda works. Depending on the tone setting the radio audio bleeds through either from the detector diode or the tone circuit. So I've been thinking about it and it might be a good idea to somehow kill the radio signal. Either open the cathode circuit of an rf stage or switch to the Police band.

[MrFixr55]

You can use a DPDT switch.  One pole to switch Audio Input from radio to Aux, the other to short the output of the radio (Junction of C50 and R51) to ground.  This does not damage the circuit because the output resistor is 100K Ohm.

I m a little too uncoordinated and a little too lazy to draw the circuit, but here is a sippet from the Zenith 6S27 / 6S52 Schematic showing the idea
   

[Tiddat33]

Thanks for the help!  As suggested it sounds awesome… I used a switching AUX jack that disconnects the radio signal but I do still get some bleed over from the radio, nothing that switching over to the Police band doesn’t solve.  Thanks again!!!

[RodB]

So, I'm thinking I might be able to disable the Police Band on the band switch and rewire it to turn on Bluetooth and put a ground on the radio signal. Whenever Police Band is selected you get Bluetooth. There's nothing on that band anyway. And when the Bluetooth is powered on it turns on a blue LED.

[Arran]

I think I would use a low powered AM transmitter like an old fashioned Phonograph oscillator, the Electronics Old and New guy was working on just that, the unit picks up bluetooth from a phone, and transmits on one of the AM broadcast band frequencies. I think that's a better option then hacking into the audio amp, though adding a jack there is preferable to messing around in the band switch.
Regards
Arran