large signal stability power amplifier
I am assuming that by intermittance you meant that you have intermittent output power cutouts.
This type of intermittence might be caused by excessive current and/or voltage across the RF capacitors in the RF circuit in itslf and/or in the RF by-pass network. If it is the case the capacitor's ceramic will be slowly cooked what, over the time, will transform the ceramic into conductive material destroying the amplifier. During this process it is very commom to get some power cutouts.
PAs in 100 Watts range have considerably high current through the shunt capacitors in the output RF circuit. Did you check if the capacitors you are using withstand the current and voltage in every node of the output matching circuit? Please don't forget to check this values regarding the peak power (not RMS) to which the PA was designed for.
On the low frequency end, low frequency bypass capacitos grounds also high current maily due to sync pulses and other low frequencies components of the video signal. The same effect described above can appear here so that low frequency capacitors must be chosen to withstand current and voltage due to those low frequencies components.
In the long run, if the described above is the problem you are facing, these caps will be degrading to a point they will entirely destroy the amplifier's board, even more in high altitude sites.
NandoPG