There is a D1 and 2 in the pass F4 schematic. It originally had a 2N number for the protection diodes. That should be a 1N part number...
The above mentioned diodes prevent any input to the FET gate greater than the diode value. I don't honestly remeber the value but anything 10-15V should be fine.
Sinse Vishay bought the IR line, process, equip, and all, I would suppose the originall Vgs max is the same as it always was? (20V). Not 30V! that is likely a mistake. However, irrelavant. Any more than a few V above the necessay signal level is a waste. We are not trying to get low on resistance here.
The above mentioned diodes prevent any input to the FET gate greater than the diode value. I don't honestly remeber the value but anything 10-15V should be fine.
Sinse Vishay bought the IR line, process, equip, and all, I would suppose the originall Vgs max is the same as it always was? (20V). Not 30V! that is likely a mistake. However, irrelavant. Any more than a few V above the necessay signal level is a waste. We are not trying to get low on resistance here.
Well, it sounds like you understand. And there are a few making the same question recently on other threads???. The zeners in the schemo are there to protect excessive high (>20V) Vgs from burning a hole in the oxide between the Gate metal (gate connection) and the channel(source in this dicussion). Once you burn a little hole in that oxide, the MOSFET is not what you think it is anymore, and is likely a permanant short! The first and formost protection Andrew is suggesting is likely correct. Just don't blow off those G-S diodes unless you know what your doing. less than 20V is a good Idea but more than 5V is probably also good. I like a 14V zener '-) Arguably, the next most important parameter is how hot those suckers are? How much bias you set it up for? Hotter is better to a point. The point where you've lost control and you melt the channel... 
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