[Hallicrafters] SX-28 S-meter adjustment

[Bill Gerhold]

Almost sounds like a polarity change.  I would change the "S" meter tube.

K2WH

-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of Julian Bunn
Sent: Monday, March 26, 2007 10:41 PM
To: Bill Gerhold
Cc: HallicrafterSX28 at aol.com; Hallicrafters at mailman.qth.net
Subject: Re: [Hallicrafters] SX-28 S-meter adjustment

Hi Bill,

Thanks for the thoughts ... the needle swings further right than the no 
power position,
so it is not a case of the circuit losing power. I need to make some 
more voltage
measurements, to understand what is going on.

Julian

Bill Gerhold wrote:
> The first and second paragraph of your posting sounds like the normal
> movements of the "S" meter.  I have an SX-17, that does exactly the same
> thing with the AVC on and off as you describe.
>
> The meter swinging hard to the right, sounds like the resting position of
> the meter when the receiver is not powered up.  All (as far as I know)
> Hallicrafters "S" meters peg to the right when powered down IE no voltage
on
> the meter.  It almost sound like an intermittent AVC switch, an
intermittent
> "S" meter winding or intermittent "S" meter internal connection.  Check
> these items.
>
> K2WH    
>
> -----Original Message-----
> From: hallicrafters-bounces at mailman.qth.net
> [mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of Julian Bunn
> Sent: Monday, March 26, 2007 1:33 PM
> To: HallicrafterSX28 at aol.com
> Cc: Hallicrafters at mailman.qth.net
> Subject: Re: [Hallicrafters] SX-28 S-meter adjustment
>
> Actually I am beginning to think my problem isn't anything to do with
> the S-meter. I have checked the S-meter pot, the 100 Ohm parallel
resistor,
> and the voltages around the S-meter tube, and everything looks fine.
>
> The symptoms of the problem suggest something wrong in the AVC circuit.
>
> With AVC off, the meter needle hovers around the zero (leftmost) position.
> If I tune in a strong signal on the BCB, then the needle moves a little
> higher. If I then turn the AVC on, the needle moves up the scale
> and starts indicating something plausible as a signal strength.
>
> (As I understand from the manual, the S-meter reading is only valid with
> AVC on.)
>
> However, after a short while, the meter needle swings off hard to the
right.
> Sometimes
> this happens almost immediately after turning on the AVC, and sometimes
the
> needle hangs around for a few seconds before swinging off.
>
> If there is no strong signal tuned in, the meter needle does not do this.
>
> It's almost as if there is some delayed feedback, and the AVC is too
> "aggressive".
>
> Any comments much appreciated.
>
> Julian
>
> HallicrafterSX28 at aol.com wrote:
>   
>> Check the S-meter pot most of them get shorted .Remove the S-meter pot
>>     
> check 
>   
>> resistance from any of the terminals to casing.
>>  
>> By the way The S-meter is adjusted to zero with the AVC off doesn't
matter
>>     
>
>   
>> whether the antenna is connected or not .
>>
>>
>>
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>   
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