JBL Olympus C-50 loudspeakers

A Marantz 8B tube amp with its 35wpc will drive those JBL's moderately well!

The Marantz is a Model 7 and I don't know if my Dad did the conversion to model 9 or not. The speakers are playing radio with a old Pioneer SX 450

So the speakers are hooked up to a receiver and are playing music I'm not sure I understand your question? If you want to use the Model 7, which as stated above is a preamp, you will need an amplifier to pair with it.

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?