[Elecraft] Low voltage on AGC threshold

[Geoffrey Mackenzie-Kennedy]

Mike ,
Typing error in my post, last line.     Low voltage should be 2.600  not
2.667 - same as you get.  Sorry.
73,
Geoff   GM4ESD


----- Original Message ----- 
From: "Geoffrey Mackenzie-Kennedy" <gmk at gm4esd.fsworld.co.uk>
To: "Mike, W8ENG" <w8eng at arrl.net>
Cc: "Elecraft Discussion List" <elecraft at mailman.qth.net>
Sent: Wednesday, November 17, 2004 10:53 AM
Subject: Re: [Elecraft] Low voltage on AGC threshold


> Mike,
>
> There is a design problem in this circuit, IMHO, which has to do with
> tolerances, and I am having an off list discussion about it. Nothing
> serious, and I am sure that it can be fixed easily. I'm letting you know
so
> that you don't damage anything by too much poking around in K2. The 3.78
> volts that you read at U2 pin 5 is 0.053 volts higher, I figure, than you
> should get with the 7.8 volts from the 8v regulator, if the RP6 resistors
> are 5100 ohms +- zero!! Three terminal voltage regulators also have
> tolerance specs on voltage output as measured at the regulator output
> terminal, so 8.000 volts is not a sacred cow.
>
> I had exactly the same sort of problems, slightly different voltages. But
K2
> was VERY useable with AGC on, but not quite up to full sensitivity being a
> little bit "AGC limited".
>
> 73,     Geoff    GM4ESD
>
> PS : The low voltage that you get is 2.6 volts  -  I figure that you
should
> get 2.667 volts - nit pickey fussy eh?
>
>
>
> ----- Original Message ----- 
> From: "Mike, W8ENG" <w8eng at arrl.net>
> To: <elecraft at mailman.qth.net>
> Sent: Wednesday, November 17, 2004 12:44 AM
> Subject: Re: [Elecraft] Low voltage on AGC threshold
>
>
> > This is an update to my earlier post.  I touched up a solder joint and
> > reassembled the radio.  The voltage on pin 5 of U2 was still 3.78 volts,
> > with the RF gain set fully clockwise.  The input voltage from my pow