[Hammarlund] HQ-129-X Question

[Bob Macklin]

I have located the capacitors in the LO that are probably causing the 
problem.

BUT!

They are under the bandswitch and impossible to get to without major work.

So I am going to just leave it like it is. I just use this receiver to look 
around the bands to see if or where the activity is. But I have been 
thinking of pairing it with a Johnson Ranger.

Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark"
----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: <kgordon2006 at frontier.com>; "Bob Macklin" <macklinbob at msn.com>
Cc: <Hammarlund at mailman.qth.net>
Sent: Monday, November 29, 2010 3:57 PM
Subject: Re: [Hammarlund] HQ-129-X Question


>
> ----- 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
>