skysurfer wrote:For those who just watching this topic, any clue on how this mod was made? What would it take to reinstall it to the original speeds?
If memory serves -- and it's a long time since I've been in the innards of a PR99 -- the machine's speed pair is basically determined by the diameter of the capstan motor shaft. So to modify the machine to run at 7.5 and 3-3/4, for example, you'd need to acquire the appropriate replacement shaft, then remove the capstan motor from the chassis, disassemble it to swap out the capstan shaft, and then put it all back together...
...but a different shaft diameter would obviously affect the tape path to some extent. I can't remember whether the capstan motor position is adjustable or not... but I imagine it's likely you'd need to realign the head positions and other transport components after the refit.
And once all that is done, you'd then need to modify the record/replay EQ curves and levels for the higher speed standards and realign the electronics accordingly.
In other words... it's wouldn't be a trivial job.