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37-630 Aux Audio - Printable Version

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37-630 Aux Audio - JohnJarratt - 10-31-2017

Hi:  I'm installing an  aux, audio connector to my  37-630 and I 'm running into an issue.    Using the attached photos as a guide  I  cut the connection to the top of the volume pot between it and cap #40 and  and  made the connections the same way I have done it on  a few other radios (see the blue outline).The signal from the Mp3 player goes through when it is connected  into the aux.  The radio stations play fine when the Mp3 is disconnected. The problem is that when I am on a radio station and connect the Mp3 I can still hear the station over the Mp3 signal.   There must be another path that is allowing the radio to play even with the MP3 connected.  The connector itself is the type that should disconnect the signal  coming from capacitor #40.  I experimented and disconnected the  #40 cap entirely  so that there is no radio signal coming from that line but I can still hear  the  radio station  albeit at a lower volume.  I am wondering how the station is still getting to the audio amp and if there is anything I can do that will allow  the aux connector to be used without reducing  the radios performance. Thanks for any ideas.

RE: 37-630 Aux Audio - JohnJarratt - 11-01-2017

My theory is that the radio signal is getting through by the direct connection between the primary of the second IF transformer (37) and the primary of the output transformer (57). Maybe that would explain its low amplitude. Does anyone see this as a possibility?

RE: 37-630 Aux Audio - vinzer - 11-01-2017

You might try grounding the joint of resistors 39 and 41 to see if stops audio from the radio.

RE: 37-630 Aux Audio - Radioroslyn - 11-01-2017

Hi John,
> Does anyone see this as a possibility? 
No not so much.
I think what you are experiencing is leakage from the diode section over to high gain triode section. It's a fairly common thing on sets that use a 12AT6 or 12AV6. When you turn the volume all the way down you still the set playing a little
Would try a different 6Q7 and see if that helps. You could lower the value of 41 say to 220k or so but this will lower the volume of the radio a little.

RE: 37-630 Aux Audio - JohnJarratt - 11-01-2017

Gave that a try but it accomplishes the same thing as disconnecting cap #40.  It removes the signal from the IF secondary but there is still a residual output getting to the audio stage.

RE: 37-630 Aux Audio - JohnJarratt - 11-01-2017

Thanks Terry:  I knew it had to be something Icon_smile.    I tried a couple of other 6Q7's with the same result. The MP3 sounds fine as long as the radio is tuned off a station so I won't be going any  farther.