[Tech-Assist] MRF 151g - troubles

[wpio]

I have replaced them in FM pallet amplifiers and have had 
success.  In this case, it's a P-tek 500 watt amp.

But now, I'm failing.  They flashed out about a minute of 
operating ok.  ($120 each - outch)

Are there some secrets to installing these?  Would someone 
tell me if I could be damaging them by using a 700 watt tip 
in the Weller?   I make it a point not to linger the tip 
after the solder is molten.

Randy