Hello fellow 16XL owner!!
Glad to hear yours is working so well... ( mine is not, No color via tuner, was the orig prob when I got it, then it sat for many years... )
First and foremost, in order to keep the FB safe cool and happy ( as I have seen it stated many times )
run through the horizontal sweep circuit adjustments ( page 7 under Misc, adjustments )
MOST important is the cathode current on v12 horizontal output.