[Hallicrafters] Audio distortion when AVC is 'OFF'

[Craig Roberts]

As Don pointed out, the AVC "off" setting is used when aligning the receiver
so that the automatic volume control does not yield misleading signal output
readings. But, the "off" position is also useful when copying CW (Morse
code).  Engagement of the AVC, unless an especially fast decay setting can
be selected on your receiver, can cause a CW signal to "pump".   Turning the
AVC off and attenuating the RF Gain for listening comfort often yields a
much more pleasant result. The AVC off/manual RF Gain method can also help
reduce the degrading effects of noise and annoying adjacent signals.

In short, there's absolutely nothing wrong with your radio -- and there's
absolutely nothing wrong with turning the AVC off and and playing with the
RF Gain control if that means better listening. That's why the engineers
made it defeatable to begin with.

73,

Craig
W3CRR




----- Original Message ----- 
From: "Don Ehrlich" <ehrlich at olypen.com>
To: "Olaf Madsen" <Olaf at carolina.rr.com>; "hallicrafters"
<hallicrafters at mailman.qth.net>
Sent: Monday, March 01, 2004 11:56 AM
Subject: Re: [Hallicrafters] Audio distortion when AVC is 'OFF'


> Sounds normal to me.  Without AVC a loud station will overload the
> detector and cause distortion.  Turning the RF Gain down manually
> reduces the gain of the RF preamp stages ... essentially what the AVC
> does automatically when in the AVC ON position.
>
> When listening to an AM station one would normally have the AVC turned
> on and the RF gain all the way up.  I have never found a use for the
> AVC OFF position except (and this is important sometimes) when
> aligning the receiver.
>
> Don K7FJ
>
> --------------------------------------  orig
> msg -----------------------------------------
>
> I have ''restored'' a number of Hallicrafters receivers (SX-28,SX
> 42,SX-43 )and also some National's.---They all run pretty well, but
> show the same symptoms.----
>
> Normally the receiver is run with the RF Gain all the way up and the
> AVC in the 'ON' position.-----When turning the AVC to  'OFF',the
> volume increases on the strong stations and the Audio gets quite
> distorted.---this can brought back to normal (no distortion) by
> turning the RF Gain down.---The point at which this happens,is very
> distinct as you turn the RF Gain down.-----This symptom occurrs on all
> of my receivers.
>
> ---Question,---Is this normal ????---- Or have I missed something
> while ''restoring'' those Radios.---They have all been
> ''re-capped'',but I normally leave the resistors alone and check the
> tubes by substituting with others I have in the Junkbox.
>
>
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