[Hallicrafters] S20-R band 4 LO warble

[Carl]

Rewiring the socket for a 6SB7Y will improve sensitivity and should help 
stability, Ive noticed a big improvement on the HQ-129X.

The problem with a 6K8, 6SA7 or any converter tube is that when it includes 
the LO the space charge between the oscillator and mixer sections creates 
that wobble effect. When the tube is used just as a mixer the effect is 
absent but there will often be some pulling of the seperate LO tube on 
strong signals.

The 6SB7Y was developed for the early 42-50MHz FM band and is the best in 
the octal category. The next step would be going with a 9 pin miniature such 
as the 6X8 and has been written up for the HQ-129X but is easily adaptable 
to most sets.

Carl
KM1H




----- Original Message ----- 
From: "James Liles" <james.liles at comcast.net>
To: <hallicrafters at mailman.qth.net>
Sent: Tuesday, July 26, 2011 9:02 PM
Subject: [Hallicrafters] S20-R band 4 LO warble


> Hi Richard and Paul:
>
> The 6K8 LO in the S20-R, SX24, and SX-25 create a ratty note or for lack 
> of
> a better word Warble on band 4.  A spectrum analyzer shot of the 
> oscillator
> on band 4 looks like a jagged waterfall kinda like a bunch of gerbils
> running in a treadmill with the a bunch of marbles on a tin barn roof!!! 
> It
> is not a result of physical movement or jarring.  The output is pristine 
> on
> the other bands.  Don`t want to make major mods --- It`s my original
> receiver --- maybe just a change of the 6K8 to something else.
>
> Kindest regards Jim K9AXN
>
>
>
>
> -----Original Message----- 
> From: Paul Daulton
> Sent: Tuesday, July 26, 2011 5:09 PM
> To: james.liles at comcast.net
> Subject: Re: [Hallicrafters] S20-R band 4 LO warble
>
> My memories of SX24 and 25 from High School days that was cured by a
> new 6k8 mixer. S 40 used a different tube for the first mixer.
>
> Paul k5wms
>
> Quoting James Liles <james.liles at comcast.net>:
>> Do the S-40 or S-40A receivers have the warble on band 4 caused by LO
>> volatility
>> like the S-20r, SX-24 and SX-25?  At what level of receiver was the LO
>> problem
>> corrected???
>>
>> Kindest regards Jim K9AXN
>
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