please help id the missing chips!!

[ultrajosh]

I bought a home-built mixer on eBay, and it's pretty cool, built in the 70's. However, all of the channel strips are missing a few chips from the same 3 sockets. They seem to be associated with the Pan and Echo controls and the Solo/(pfl?) button. The rest of the strip (eq, compressor, buss assign) is populated with TL071's. Currently I can only use the top portion of the strips and send things out through the busses, but I want to use it as a full featured mixer (e.g. pan, stereo buss, etc).

What is the best way to figure out what is supposed to go in here? What family of chips am I looking for?

http://www.ultrajosh.com/images/HomeBrewMixer/HomeBrewMixer 046.jpg
http://www.ultrajosh.com/images/HomeBrewMixer/HomeBrewMixer 045.jpg

Here's 1/2 of the monitor section:

http://www.ultrajosh.com/images/HomeBrewMixer/HomeBrewMixer 042.jpg
http://www.ultrajosh.com/images/HomeBrewMixer/HomeBrewMixer 047.jpg

- just stick in another 741?

Here's the master section:

http://www.ultrajosh.com/images/HomeBrewMixer/HomeBrewMixer 043.jpg

Any help hugely appreciated and I can some take better pics later...

 

[arjoll]

https://homerecording.com/bbs/showthread.php?t=174231

Refer to post #10 - have you checked to see where the supply rails appear on the IC sockets? Its all very well throwing in ICs (and use at least TL071's instead of more 741s - they're pin compatible) but the small amount of extra time to check this would be well worth it. At least you know you'll be less likey to end up with dead ICs.

 

[jpmorris]

Looking at picture 2236, which has some chips in and some out, the missing ones appear to have the same connections as the 741s (or whatever they were). I'd be very surprised if they were different.

 

[ultrajosh]

progress!

I loaded the boards with TL071s and everything now works except if I put chips in the 2nd socket from the bottom. This results in horrible feedback and squealing, which changes in awfulness when I turn the pan pot, echo pan, and echo volume. So I pulled these from all the boards and I'm in bizness. Any idea why these 2 chips would cause feedback?