Jim- I just knew you had circuit brewing in your head, all good Ham Radio guys/gals do!

I'm not very good in reading schematics can you clarify the following:

1) the schematic show R2 with a value of 15.5-ohms, is that the set-point for your simulation of the 25-ohm potentiometer?

2) what does Rf at 100K do? I see it's in parallel with the MB CTS. Does it bring the values of the CTS into a range to work with R2?

If my SPAL fan is rated at 23Amps @ 12VDC, is it really feasible to drive through a large transistor?

Can I contract you to make me two of these?

Thanks in advance,

:-) neil