So...you've found a VIC-20 and can't wait to fire it up. Trouble is that it didn't come with the RF modulator.
Hey! The TI99/4A has an external RF modulator too, and the jack is the same...it oughta work, right?
Maybe. The big difference between the two is the DC voltage used to run the modulator. The TI outputs 12 Volts, but the VIC outputs only 5 Volts.
Yes, a TI modulator hooked to a VIC will work somewhat and probably won't damage anything, but it gives a very poor, washed-out image.
Using a VIC modulator on a TI, on the other hand, is not a good idea. Applying 12V to a component designed to accept 5V is just looking for trouble. It may not damage anything right away, but it's likely to at least reduce the lifespan of something.