[Elecraft] AGC Threshold Adjustment by Changing R1

[G3VVT at aol.com]

In the reply to Mike, VK1KCK I said "R1 is given as 50K preset.  In the world 
outside the USA this would indeed equate to 47K" 
 
I found that this is not quite correct as although for carbon presets and  
controls have changed to the same decade values as fixed resistors in  Europe at 
least, cermet presets which most probably Elecraft will be  using for R1, 
still retain the older values such as in this case 50K for some  reason.
 
A visual check on my K2 is that R1 when set for 3.70V at U2B-5,  being the 
optimum AGC threshold setting for my K2, the control  is not far from half 
rotation, i.e. about 25K ohms. Working out the  maths for the various resistors in 
series and parallel, including the RF gain  control to form the potential 
divider from the 8A rail comes out fairly close to  this voltage.
 
The preset R1 is as shown in the K2 Control Board schematic, maximum  
resistance for fully CCW.
 
Bob, G3VVT
K2 #4168