I would check the drive-waveforms to the base of the HOT, rise & fall times.
etc,
Of course, faulty clamping diodes in the deflection-circuit can kill it,
such as bad flyback caps, (hor deflection amplitude depends on the L
(flyback primary-inductance) together with C flyback)
A faulty flyback cap could therefore place an excessive collector voltage on
the HOT.

Tell me, will the HOT pass away directly or can you have the set going a
while?
If you're able to keep the set operational a while, I would believe most of
slow base drive waveforms.
Then you could check for fast rising temperature on the HOT.

Good luck,

Stefan

skrev i meddelandet
...
Hope you can help guys!
Have an RCA model F25163WN that keeps blowing H.O.T. What can be the
cause other
than a defective flyback?
Thanks,
Tony