I'm surprised no one pointed out that '76-'79 T-Birds' pickups are wired in series instead of parallel like '60s and "teflon" (with the blcak parts)T-birds.
This is what gives them their mid range growl. IMO those 2 pickups are way too hot in series and tend to push most amps into distortion. Call the vintage police, but I wired my '76 in parallel and like it a lot better. Could be put back to stock easily enough, though...
I've owned 'em all. There was a local music store that had a cache of '76 T-Birds that lasted until '81, I bought several at $450 a pop. Plus a few other used ones at that time for less $. Back then, I was hot for an original '64 TB IV but couldn't find one, and probably didn't have enough $ then anyway. The '76's were a disappointment to me since they are not an accurate reissue. Now I've come to appreciate them for what they are, another variation on the TB theme and cool basses in their own right.
Owned 5 real '64 TB IVs, (the first '64 was in '81 from Gruhn, who neglected to mention that someone had drilled the tailpiece mounting holes through the body, complete with countersunk 1" washers...I sent it back!) all were fantastic. The last 1 I had was so clean it was scary, I didn't dare play it...got an offer I couldn't refuse 5 years ago and sold it. Had many non-reverse TB IVs too. Now I own a '65 non-reverse IV and a '76, both sunburst.
Non-reverse 'Birds ARE great basses, (true they deviate from the original neck through body design, but nevertheless they're cool, great sounding basses...and much better basses than the non-reverse Firebirds are guitars) but the quality control wasn't so hot, some have too shallow of a neck angle, I know of at least 1 with a factory defectice truss rod...they're inconsistent. They DO have better access to the higher registers than a reverse TB, which is a big plus!
There's an issue that always comes up with '60s T birds: the bridge is too far back. Gibson blew it here, and the reason why is obvious- the (often missing) brass mute spring that was originally attached to the bridge just barely fits between the bridge pickup and the bridge, the bridge was located about 1/4" flat of where it should be to accomodate this mute. Since the bridge doesn't have a lot of travel, the intonation ends up being flat...Rotosound piano string design strings help a lot with this, by the way, and also sound really great on T Birds! Sounds crazy now, but I'm sure Gibson thought at the time that on a bass intonation innacuracy wouldn't be noticeable. That bridge pre dates the Thunderbirds (I've seen a 100% original LP bodied '59 EB-0 with a TB type bridge and tailpiece) and they weren't about to redesign it in order to put the bridge in the right place. Omitting the mute would've been the sensible thing to do, but back then a bass HAS TO have one, I suppose.
2 other issues common to all TBs are neck dive and fragile headstocks. The answer to the first is the right strap. A wide padded strap won't slip (avoid any strap with a sliding pad!) on your shoulder and will hold the bass in place. I find that the right strap will completely eliminate neck dive! You can take your hand off the bass and it'll sty put! I've seen countless T Birds with multiple neck screw holes from someone trying to find the Magic Spot where it'll balance...don't try it, doesn't work!
As for the fragile headstocks, BE CAREFUL and use strap locks!
Thunderbirds are fantastic basses, but aren't they perfectly thought out marvels that a Fender bass is. Still, they possess a unique tonality that can only be achieved with a TB, not to mention how cool they look!
I love 'em all, but having owned all 3 variations, I must say that the original reverse T-Bird is my favorite...no question.