I THINK some quad Pioneers may have a sub out, the stereo SX-6000 does and it's about a 1971-3 set?
Maybe not what you are looking for and at that age transistor noise and cap problems as well as shorting switches can plague them sometimes.
Steven,
The pioneer sx-6000 was a stereo receiver and it did have a center channel out but no sub out. had one.
Pioneer quad units used prefix QX. I don't recall any that had a sub out jack.
All these av units etc that have a sub out jack, most just have a fixed 80hz band pass filter built in. Thats all it is.
Still requires a outboard amp to drive the sub woofer.
You can add a band pass or crossover to any preamp or receiver that has a preamp out. by adding a y connector to
split the pre amp out signal to the input of the main amp and to the input of the sub amp.
But its nice to have a preamp that has two outputs, just less cables.