[Hammarlund] HQ-129-X Question

[Richard Knoppow]

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "Bob Macklin" <macklinbob at msn.com>
Cc: <Hammarlund at mailman.qth.net>
Sent: Monday, November 29, 2010 3:44 PM
Subject: Re: [Hammarlund] HQ-129-X Question


> On 29 Nov 2010 at 15:12, Bob Macklin wrote:
>
>> On any single band there are only 3 frequency determining 
>> components.
>> The tuning capacitors which should not change with age. 
>> Especially the
>> Hammarlund variables. The inductor which may change a 
>> little with time
>> and the trimmer.
>
> In many receivers (and transmitters) there are also 
> parallel padding
> capacitors, usually fixed micas.
>
>> The only one that has an effect on the linearity between 
>> the end
>> points is the main variable.
>
> Well, James Millen, among others, might argue with you 
> about that. :-)
>
> I think linearity, with regard to the main-tuning cap, has 
> more to do with the
> SHAPE of the variable capacitor plates, although the 
> relationship between
> the main-tuning cap, the inductor, and the padding caps 
> comes into play too.
>
> According to a couple of articles I have read on the 
> subject, one by Millen,
> another by Langford-Smith in "The Radiotron Designers 
> Handbook", linearity
> in a capacitor-tuned circuit is VERY difficult to achieve 
> as there are, quite
> simply, too many variables involved. It often isn't 
> economically reasonable to
> go to the max.
>
>> And I doubt it has changed a measurable
>> amount.
>
> You're absolutely right, of course.
>
>> I am having similar problems with my NC-109. I have bands 
>> B and D very
>> close. Close enough for a receiver with a string drive.
>>
>> But I cannot get band C close to the manual. I can make 
>> it correct at 5MHz
>> ( the bottom) and 7MHz but not at 14MHz (the top).
>
> To my mind, since it is right on on bands B and D, and not 
> on band C, then
> the tuning cap cannot be the problem. Therefore, it has to 
> be something in
> the circuit unique to band C.
>
> Possibly a shorted turn in the inductor?
>
> A fixed mica padding cap gone bad on ya?
>
> Powdered iron in the inductor (if there is any) gone weird 
> on ya?
>
> All of which, although very rare, I have run into at least 
> once in my almost 56
> years in electronics.
>
>> I am going to try and get it close between 5MHz and 10MHz 
>> and ignore
>> the portion above 10MHz.
>
> Well, if you are anything like me, it will still keep 
> bugging you, yeasting
> around in the back of your mind, sometimes for years, 
> until you figure it out
> and get it fixed. ;-)
>
> Ken W7EKB

     Padders can cause this problem. I've encounterd bad 
padders even in a SP-600-JX. That receiver used quite 
precise padders in some of the oscillator modules. If off 
they will cause a bump in the calibration. The HQ-129-X has 
a number of padders. I suspect some may have drifted. This 
would affect the calibration at the center of the band when 
the end points were set correctly. They would not affect the 
band spread calibration.
     Even silvered mica caps, which are among the most 
stable of all types, can go bad and should not be ignored 
simply because failures are relatively rare. This equipment 
is getting _very_ old now and it is a tribute to the quality 
of design and construction that it still works at all, let 
alone works quite well.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com