[Hallicrafters] Anyone added padding to an SX-24 or SX-25?

[Carl]

Ive improved the top 1 or 2 bands on a few receivers by changing out the 
input coil with a low loss, high Q toroid.

Its a hit and miss operation if you dont have access to some test 
equuipment inorder to duplicate the secondary inductance very close. I 
use a late 70's era military Q Meter which was a $35 Ebay find.

Most Hallis suffer from the lack of an antenna trimmer which compensates 
for tracking and antenna issues. This can be added either externally or 
internally using an unused front panel feature to control a rear of 
chassis variable cap.

Also those receivers are designed for a high impedance input and a 50 
Ohm antenna will degrade performance without either a tuner or 4 or 9:1 
balun. Most TV baluns will work on Band 4.

BUT, first make sure your tracking alignment is correct.

The last step would be improving the RF stage as even in as new 
condition the SX-24 was rather deaf above 20M.

Carl
KM1H



----- Original Message ----- 
From: "SX-25" <telegrapher at hotmail.com>
To: <hallicrafters at mailman.qth.net>
Sent: Thursday, April 02, 2009 9:43 AM
Subject: [Hallicrafters] Anyone added padding to an SX-24 or SX-25?


> Been experimenting with the "elusive" band 4 on a Hallicrafters SX-25. 
> I've already added the
> extra turn on the RF coils with some improvement but not sufficient to 
> exclaim "EUREKA!" So my guess is that a design modification must be 
> done to coerce reasonable results out of band 4. Note here I am 
> seeking "reasonable results." I am not unrealistic enough to think I 
> am going to turn the SX-25 band 4 into a red hot performer. I would be 
> content with "reasonable."
>
>>From the superb book, Radiotron Designers Handbook I have been able to 
>>extract the formulas for adding padding to a receiver. It is a pretty 
>>straight forward procedure and, other than getting the instruction 
>>book out to figure out how to run all the algebraic functions on my 
>>pocket calculator, seems not to be too daunting. In fact, interpreting 
>>the pocket calculator's instruction book was more of a head-scratcher 
>>than the whole 3 pages devoted to IF tracking and padding calculations 
>>in Radiotron.
>
> Has anyone else attempted to approach the tracking problems of an 
> SX-24 or SX-25 with padding capacitors? I'd be interested in comparing 
> notes and sharing information.
>
> WA9VLK
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