JBL Olympus C-50 loudspeakers

Do the speakers have a wire coming out of them to plug into the wall ac outlet? If so, then the speakers have an amplifier built in (very rare). If not, then you will need an amp to use the model 7 preamp. The Pioneer SX450 does not have a separable preamp/power amp, so you can't use it with the Marantz 7 preamp. I'm a bit confused, do you have a Marantz model 8? Very nice system.

@eltabor,
The Marantz Model 7, is a preamp, the Marantz Model 9, is and amp.
What conversion are you thinking he did? As jond has said, you are playing music with the Pioneer SX 450 receiver hooked up to the speakers so what is the problem you're experiencing?

There is a plug built in to the Solid State Energy Transducer. Dad wanted to exchange the marantz model 7 for the model 9. Being on Wake Island made that cost prohibitive for Marantz. They supplied every thing needed for the conversion, but I don't know if he did. I'm trying to find out if everything is functioning properly so I can try to sell all of this. I don't have room for them and I don't want to put them in storage.

@eltabor,
Do the back of the JBL's look like the link below? Mike

https://worldradiohistory.com/hd2/IDX-Audio/Archive-Stereo-Review-IDX/IDX/60s/HiFi-Stereo-Review-196...

that photo is the solid state transducer. I have all the manuals and catalogs from the time period. It's the S8 speaker configuration.