[ARC5] More newbie questions

Wed, 05 Feb 2003 22:30:43 -0600

"But I'm looking at a schematic of the BC-454"

That makes a difference then.  This is from the SCR-274N manual 15 Feb, 
1943:

"The control grid of r-f amplifier tube V-3 (Tube VT-131) and of the first 
i-f amplifier tube V-5 (Tube VT-131) are returned to ground through a common 
resistor, R-11, in the control grid circuit of the second i-f amplifier tube 
V-6 (Tube VT-131).  The object of this auxiliary gain control circuit is to 
prevent overload of the r-f and i-f amplifier by signals producing as much 
as 2 volts in the antenna circuit.  In effect, it is an automatic gain 
control which is operative only on signals so strong that they would 
otherwise overload the receiver.  When an overload condition arises, the 
second i-f amplifier grid current flows through R-11, making the grid side 
of R-11 negative with respect to ground.  By connecting the grid circuits of 
the r-f and first i-f amplifier to this potential, the gain of these tubes 
will be reduced to the point where overload in these stages is prevented.  
This circuit does not limit the maximum volume that can be obtained from the 
receiver.  The output will be essentially uniform for r-f input signals 
stronger than 100 microvolts (and up to 2 volts)."

Sean

>From: Jim Mandaville <[email protected]>
>To: [email protected]
>Subject: Re: [ARC5] More newbie questions
>Date: Wed, 5 Feb 2003 20:48:47 -0700
>
>Sean writes:
> >
> >It looks like there are two AVC lines in the ARC-5 receivers.  The 1st 
>AVC
> >controls the RF amp and 1st I.F. amp and is taken off of the diode plate 
>in
> >the 12SF7.....
>
>But I'm looking at a schematic of the BC-454, which doesn't use that tube.
>In my diagram the only tube with diode plates is the 12SR7 (detector and
>BFO).  One of the two plates is used as a normal detector.  The other one
>is simply grounded.  I don't see any connection between the detector diode
>and what appears to be the AVC line ...
>
>Jim
>
>
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