[Elecraft] K2 AGC low voltage

[Don Wilhelm]

Mark,

The 8 volt regulator is a 10% tolerance part, and as of late, they have 
been running on the low side of the nominal voltage.  7.56 volts is well 
within the device specs.  A replacement regulator from Elecraft may or 
may not provide a higher voltage.

The maximum AGC Threshold voltage is directly related to the 8 volt 
regulator output voltage since the voltage is simply a 3 legged 
resistive network.

The major 'problem' with the lower AGC Threshold is that at lower 
voltages, the S-meter adjustments get a bit 'squirrelly'.  Meaning that 
it may not be possible to adjust the S-meter to indicate an S-9 level 
with a 50 uV input and an S-1 level with a 1 uV input (XG1 or XG2 signal 
generator).  The performance of the K2 will not suffer as a result of 
the lower voltage.

My advice is to simply set the AGC Threshold to maximum in your case and 
if you experience S-meter difficulties that are important to you, then 
changing the 8 volt regulator and re-doing the AGC Threshold followed by 
CAL S LO and CAL S HI would be in order.  If you are one of those hams 
who consider the S-meter to be only a relative indicator of signal 
strength rather than an absolute scale, then you will not have any 
problems with your current 8 volt regulator.

73,
Don W3FPR

Mark Mellish wrote:
> Hi K2 builders,
> I'm working on K2 #6318, and the voltage at pin 5 of of U2 is maxed 
> out at 3.61v.  The 8v regulator is only putting out 7.56v.  I see some 
> posts in the archives recommend replacing the regulator, and a couple 
> that say to leave it alone, and all will be well.  Is there a final 
> word on this?  What is the tolerance on the regulator?  I would much 
> rather change out U4 now rather than later.  Will Elecraft likely have 
> an 8v replacement, or will it just be luck?  U5 is putting out 4.95v.
> Thanks, Mark
>