When I build the stereo decoder, I would like to try to salvage this chip out of some junk electronics. Does anyone know the most likely types of equipment to look for in trying to scavenge the LM1800 ic out of it?

Both the LM1800 and the very similar LM1310 were only used in FM stereo tuners and receivers. There's not much use for them anywhere else since they were specifically designed to demodulate a composite base-band signal into L and R stereo audio.

Dave

Did they ever use them in stereo televisions?

I have three LM 1800's, and two LM 1310's that have never been used.

Yours for a padded SASE; I've tried sending components in a regular envelope in the past with disastrous results, so need a padded one.

PM if interested.

PM sent

...AFAIK, no. I believe stereo TV sound is a somewhat different animal than FM stereo and requires its own specific decoding system...

The LM1800 could be made to work for TV stereo. The pilot frequency was equal to the horizontal line frequency (15.7 kHz) instead of 19 kHz. So there were some minor component changes required. However the big problem was that TV stereo used a noise reduction system (DBX, I think) that required special audio processing ICs, and so typically, the entire stereo decoder and noise processor were all put on the same chip. Even so, there was a TV stereo decoder construction project in the mid 1980's in Radio-Electronics magazine that used an LM1800. Since the audio processor chip was generally unavailable to hobbyists, they came up with a different but reasonably compatible audio processor. I built the decoder, and it worked very well. I still have the circuit board in my junk box, but the LM1800 was pulled for another project and I don't know where it ended up.

which was the same as what was used for video sine-wave encoding of OTA pay-tv stations...

Thx for reminding me why I had bought these chips, lol;

...now that you mention it, I believe you're exactly right about the dbx. If that was anything like the dbx noise reduction they had for tapes, that meant the audio was heavily compressed before encoding at the transmitter end and had to be re-expanded after decoding at the receiver end. I'm venturing an educated guess that the R-E project used some op amps in some sort of voltage-controlled amplifier arrangement after the LM1800 to do the expansion...

I just had another look. In addition to the LM1800 stereo decoder, it used an NE570 compander chip for the audio de-compression, and four LM358 dual opamps for other miscellaneous functions.