[Hammarlund] Unstable Oscillator adjustments in the HQ-180

[Richard Knoppow]

    Interesting, I have two SP-600s and have never had problems setting 
the oscillator frequency. The trimmer is an air capacitor and pretty 
stable. I use a plastic tool with a metallic blade that is part of a 
military tuning tool. Setting the coils really requires a tool with a 
blade in socket so it won't slip off the slot.  These used to be common 
commercial parts but no more.  I have a tool from an RCA AR88 that is 
ideal and would work for the SP-600 trimmer caps too. I suppose you 
could make one. The RCA tool has a blade on one end and a socket with a 
recessed blade on the other end.
     My SP-600s have a problem with microphonics that I have never been 
able to track down. Its not the oscillator tube although the 6C4 is 
notorious for this.  I have a rebuild job sitting on the back burner and 
have a couple of things to try.

On 2/2/2016 10:24 AM, Al Parker wrote:
> Hi folks,
>    I think maybe Ed & Roy have it explained.  If it's stable at all 
> time except when making an adjustment, or getting something metallic 
> in the area, it's pretty normal.  Ron, you said you're using it in the 
> CX, is it working OK under normal usage?  If you want to hear 
> something squirrelly, try setting the osc. of an SP-600, up at 6 
> meters ;-)
> 73,
> Al, W8UT
>
>
> ----- Original Message ----- From: "Roy Morgan" <k1lky68 at gmail.com>
> To: <djed1 at aol.com>
> Cc: <hammarlund at mailman.qth.net>; <Ron.K3PID at sbcglobal.net>
> Sent: Monday, February 01, 2016 11:47 PM
> Subject: Re: [Hammarlund] Unstable Oscillator adjustments in the HQ-180
>
>
>
> On Feb 1, 2016, at 9:35 PM, djed1--- via Hammarlund 
> <hammarlund at mailman.qth.net> wrote:
>
>> I suspect what you're seeing is normal. Remember, when you're tuning 
>> an IF of 455 KHz, an adjustment of say 1 KHz is 1/455.  If you're 
>> adjusting the oscillator to the same tolerance, the ratio is (at 20 
>> MHz) 1/20,000. So it is a lot harder to adjust the HF oscillator.  I 
>> definitely avoid using an output meter to adjust the HF oscillator.  
>> I either use the BFO, aiming for zero beat with the generator, or I 
>> couple a frequency counter to the oscillator and set it that way. And 
>> any of my Hammarlunds will shift the oscillator frequency a bit when 
>> you put a metallic screwdriver on the trimmer.
>> Aslong as it is stable when you're done, you probably don't have a 
>> problem.
>
> I think Ed is right.
>
> First, When tuning an IF can for peak you are dealing with a low 
> frequency tuned circuit, and moving it’s resonant point around a title 
> bit.  When you do the alignment on the local oscillator coil, you are 
> dealing with a higher frequency oscillator and you are changing it’s 
> frequency.  As it passes the point you want, it peaks the output and 
> zips past it quickly so finding the peak is difficult.  Ed’s 
> suggestion about the zero beat is good… it will be easier to use than 
> a peak in the receiver output.
>
> Second, if you are able to use a NON-metalic tuning device, your life 
> will be easier.  As Ed mentions, the metal end of the timing tool 
> changes the frequency of at the oscillation.  Well made chop sticks 
> (not the split-apart throwaway ones) make fine tuning tools.  Just 
> sharpen with a jack knife, or a file.
>
> Roy
>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL