I was flying VOR to VOR in a 727-200, and everything was working fine; then, I reached my next waypoint and tuned the VHF Nav (both radios, just to be sure) to the next VOR station. Everything appeared to still be working, but then ATC vectored me to the right, even though the HSI said I should be flying left to intercept the VOR. I checked the GPS and it said that I was way to the left of the VOR course. Am I doing something wrong, or is my HSI messed up?

Thanks,
boeing247