[Elecraft] K1 AGC Mod revisited

[Tom Althoff]

Ron ZL1TW and I have been bemoaning the slooooow recovery time of the AGC that we were experiencing with both of our K1's.   

Ron's been doing some experimenting as have I using componants from out junkboxes.

What we ended up with was changing C31 from a 2.2ufd cap to a 0.22ufd cap.

Ron added a 47k resistor between pins 9 and 10 of RP3.    I had a 22k here and used that value in my K1.

We then changed C67 to a .01.   Basically it became an RF bypass cap rather than any kind of AGC timing cap.

I would now describe the AGC time constant more along the lines of the "slow" agc setting of the K2 but much quicker than the stock K1.   

Additionally, in MY K1 I added a 0.47ufd cap in series between the /AGC OFF line and the positive side of C31.    When I turn "OFF" my agc the time constant gets greater and sounds closer to a stock K1.   A 1ufd or even the original 2.2 from c31 or C67 could be used here.   I never use the K1 with the AGC off so this gives me a rudimentary "Fast/Slow" setting on my AGC.    

Of course...those of you who used the /AGC OFF line to change the brightness of the backlight would not be able to take advantage of this.  Unless perhaps "Bright background = Fast AGC,  Dim background = Slow AGC" 8-).

Neither of us are recommending that anyone else make these changes.   We're just letting people know in case there are others who find the slow recovery time of the AGC a bit too long for their liking in the stock K1.

73 de Tom K2TA
K2-TA-100 #1117
K1-4 #2146