[Amps] MOV Sizing

[Paul Christensen]

I  am planning on adding a set of MOVs to the AC line of a recently acquired Alpha 86 amplifier.  I have reviewed Littlefuse's MOV Applications Guide but I am still a bit unclear as to the optimum clamping voltage I should choose.  

I would like to use three MOVs with one placed across the 240VAC line and the remaining two placed between each side of line and GND.   I am thinking of MOVs rated at a nominal operating V of 140VAC, and 260V for the line-to-line MOV with respective clamping voltages of 180V/360V.   The MOVs would be placed directly after the fuses.  

Speaking of MOV placement, I have seen circuits were MOVs are placed ahead of the fuses or circuit breaker, but this seems like a counter-intuitive and dangerous practice.  OTOH, there are numerous designs that employ AC line RF bypass caps in front of the fuses as well but then... caps are not meant to self-destruct during a fault condition.  

Thoughts?

Paul, W9AC