UP1237 Spkr Protection Kit

[Bengali]

Hi,

I got one of these spkr prot. kits off ebay. Attached schematic.
with the 24VAC trafo, what voltage is at C4 and R1?

I have a 18VAC trafo and I don't know if that's too low or not.
What would I need to change to make it work with the 18V trafo?

Reason for the 18V trafo is it's an antek 40V that has a 12V and 18V output
so I'm hoping to use this 18V off the antek instead of another transformer.

or should a spkr protection kit always have it's own power source that
is not part of the main amp?

Thanks