[ARC5] More newbie questions

Wed, 05 Feb 2003 21:03:26 -0600

Hopefully I can answer question 1:

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.  As the receiver is tuned onto a signal, a small amount of the 
I.F. signal is rectified through this diode.  Current flows through the 
diode and through the 0.51Meg resistor (R-5) to ground.  This current 
develops a voltage drop across the resistor which is filtered by the 0.05uF 
capacitors C-15A and C-7A and is fed back to the grids of the previous 
stages to adjust the bias.

The 2nd AVC comes off of one of the diode plates of the 12SQ7 and develops 
its voltage through the voltage dividing network of 0.51Meg (R18), 0.1Meg 
(R-30), and 2.4k cathode resistor (R-29).  The voltage is fed back into the 
bottom of the 2nd I.F. transformer secondary.

Sean

>From: Jim Mandaville <[email protected]>
>To: [email protected]
>Subject: [ARC5] More newbie questions
>Date: Wed, 5 Feb 2003 18:16:03 -0700
>
>1.  Can anyone tell me briefly how the AVC works in the ARC-5 receivers?
>In the schematic I see what might be an AVC line leading to the control
>grids of the RF amp. and those of the first and second IF tubes.  But I
>can't see where it's getting the necessary bias voltage.
>
>2.  I don't think I've (knowingly) ever heard an ARC-5 CW note on the air.
>What do they sound like, say on 80 m?
>      I think I remember reading somewhere that they don't always chirp
>(actually I think a bit of chirp gives character :).  If anyone expects to
>be on the air with one soon,  perhaps they could let me know in advance so
>I can listen.  The VFO construction looks so good that it should be pretty
>stable, I'd think.
>
>Jim
>
>
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