The AM Forum

I am wondering how to record a qso or the received signal only from my boatanchors. I have a vintage tape recorder with rca input but how can i interface with the receiver? (for example a NC-300 or Hammarlund sp-600

You can use the headphone jack to the Recorder. 

The best way to do this is to use the diode output on the 600 right to the recorder.  Here are the instructions for the R390 but its the same on the 600

http://www.r390a.com/html/diode_load.html

The last option is to use a speaker to line level converter. Available at any car audio retailer. This allows factory car stereo speaker leads to be converted to RCA low level to drive an amp. Newer models actualy work very well and these are cheap.

C

On most receivers you can just come right off of the AF gain pot.  Don't come off the wiper but just end to end on the pot.  "Usually" the gain pot is one stage in from the detector and the audio is pretty clean at that point. You should have enough level to drive a line input on a tape recorder.  To use that point you must run it into a very high impedance input otherwise the coupling capacitor to the AF gain control will be not large enough and you will get LF roll-off.  Another aproach would be to come off the cathode of the prior stage or if the level is not high enough, take it off the cathode of the stage where the AF gain pot is located providing you don't have a cathode bypass cap.  Avoid running audio in the "mic" inputs of the recorder since they are extreamly sensitive and you likely overdrive it or pick up hum.  Remember to use a coupling cap if any DC voltages are present on the pick off point. 
Good Luck,
Joe, W3GMS