As for the schematic, I think all the versions had the same problem.
The main thing that changed was the turns ratio on the input transformer, they kept reducing it over the years, probably because it sounded so awful when it overloaded.
By the way, I've found a lot of other amplifiers with the same problem, it's very common when you use a collector to base cap on the second stage for compensation. As soon as the transistor turns off the cap becomes a coupling cap from the first stage to the output buffer. If the first stage still has gain and there is enough feed back, the amp flips from being inverting on the feedback to being non inverting. It then oscillates until the audio input drives the second stage back into conduction. There are a lot of power amps out there that take on a whole new cleaner sound when you move the compensation to the other side of the output stage. It adds local feedback at high frequencies, and guarantees that the gain is never greater than unity when the second stage clips. Even if it doesn't oscillate it usually recovers a lot quicker if the feedback for the integrating cap is from a low impedance rather than a high impedance.
Schematic Showing Change (GIF format)
Schematic Showing Change (PDF format)
