Its been compared to a Rickenbacker, very bright and punchy is the general tone.

However, the T40 has a lot more pickup options as you can tap the humbuckers into single coils, giving you a lot more tones to choose from.
It's closest relative (both volumes and tones on 10) would be a Wal. The slightly newer ones (from 1981 on) with rail pickups are a little brighter than the older ones with the toaster pickups, but generally have the same sound to them.

It's comparison to the rickenbacker isn't the full out tone, and it'll only do that with the pickups out of phase
1978 Peavey T-40 -> Ampeg Micro-VR - > Ampeg SVT210AV + Ampeg SVT-15E
As I recall, they were quite versatile tonally. If you are waffling about picking one up, you shouldn't worry. They are fine basses and I hereby slap a hex on Peavey for not reissuing it.
"Maybe this world is another planet's hell?" - Aldous Huxley