[Hallicrafters] Black Beauty capacitors Beware

[Jim Liles]

Hi Roger,

Same in all but using the SX-115 schematic.

The first transformer set used C73 as a bypass capacitor and to provide an RF ground reference to drive V11 the I.F. amplifier. 

The second transformer set is isolated from the B+ because it needs a DC ground reference to drive the detector and product detector.  C86 is used as a bypass and completes the tuned circuit isolating the B+ from the output.

What I forgot to add in the earlier posts was C73 and C86 have to be changed to Polypropylene.  These same capacitors although different C numbers in all of the 50Kc I.F. radios have to be changed to Polypropylene because they compound the band pass skew problem that the ceramic caps do in the SX-115 selectivity switch. 


Hope this helps Roger.

Kindest regards Jim K9AXN  


-----Original Message----- 
From: Roger D Johnson 
Sent: Saturday, March 07, 2015 2:24 PM 
To: Jim Liles 
Cc: hallicrafters at mailman.qth.net 
Subject: Re: [Hallicrafters] Black Beauty capacitors Beware 

It seem to be throughout the lines. S-76, SX-96, SX-100, etc.

On 3/7/2015 2:45 PM, Jim Liles wrote:
> Hi Roger,
>
> What model?
>
> Kindest regards Jim K9AXN
>
> -----Original Message----- From: Roger D Johnson
> Sent: Saturday, March 07, 2015 1:08 PM
> To: hallicrafters at mailman.qth.net
> Subject: Re: [Hallicrafters] Black Beauty capacitors Beware
>
> The cold ends of the first set are at RF ground due to a bypass cap. I just
> can't figure out why Halli
> would put B+ on one set of caps and not on the other!
>
> On 3/7/2015 2:05 PM, Roger D Johnson wrote:
>> I've just noticed something strange about these IF strips that I hadn't seen 
>> before. The first set of
>> capacitors on the selectivity switch have the cold ends connected to B+ while 
>> the second set has
>> the cold ends grounded. Anyone know why Hallicrafters did this?
>>
>> 73, Roger