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K2 AGC low voltage

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ve7ymm

K2 AGC low voltage

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

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Don Wilhelm-4

Re: K2 AGC low voltage

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
>