[ARC5] need advice on Tx tracking adjustment

[Bill Cromwell]

Confusion!

My take is that the tuning *range* falls 4 kc too short. One of the two 
adjustments increases or decreases the range (usually the low frequency 
one). So if the range is short adjust it to make the range longer. Then 
use the other one to set 'zero'. You usually have to work back and forth 
to get it closest. If you move the low frequency  adjustment just to 
point where the low end reads exactly 'on' you will be going back and 
forth a lot longer and maybe never get there.

I hope this helps - if I understand right. If Les's interpretation is 
right then you should be able to just set zero - probably the high 
frequency adjustment. Did you say it does gave enough adjustment to get 
there? Look at stretching out the range.

Over the years the number of pF and r changes in many of the parts. Some 
of those parts influence the oscillator frequencies. They may have to be 
replaced to get your oscillator(s) back in spec.

73,

Bill  KU8H

On 08/20/2016 02:45 AM, Leslie Smith wrote:
>   Hello Jim,
>   I need to check my understanding.
>   Do you say that at every point on the dial the frequency is "off" by 
> exactly 4.0kHz.
>
>   You used the words, "end to end" - and these words give that idea.
>   If that is the case, the dial itself is out of calibration.
>   The set itself is accurately set up.
>   If so case there should be a procedure to leave the oscillator tank 
> components untouched and simply adjust the dial mechanism.   That's my 
> take on this. The problem seems to be related to the first point you 
> made - that the locking screws were corroded in some way.
>
>   However, my conclusion depends on my assumption - and that may be wrong.
>
>
>    BW & 73 de Les Smith
>    vk2bcu at operamail.com
>
>    o-o-o
>
>
> On Sat, Aug 20, 2016, at 14:21, J Mcvey via ARC5 wrote:
>> This particular BC-696 was supposed to be "government refurbished" in 
>> 1953. It was on a single  rack wrapped in heavy plastic.
>> The only problem was that whatever they used to clean it was not 
>> properly rinsed, so over the years in the bag, it ate the lock knobs and
>> some of the case screws!
>> Fortunately, the innards were OK.
>>
>> The problem is that the tracking is off 4 khz from end to end. The 
>> specs say that it should be within 200-300 cycles.
>> The osc trimmer was nearly all the way out of mesh, so I didn't have 
>> enough adjustment to bring it up to where it needed to be.
>> I set the trimmer at 50% and adjusted the main osc cap. That got it 
>> on frequency THERE, but the tracking is still go good
>>
>> This stuff is notoriously tricky , so I consulted the manual.
>> Page 57 (of manual-PDF page  71) describes the process , but is very 
>> vague, talking about "changing the dial to the other side of the 
>> lowest frequency mark at a point about
>> 1 1/2 times from that mark as observed..." WHAT???? This make no 
>> sense to me!
>> Can someone explain what they mean in a coherent way?
>>
>> Is it:
>> 1) adjust to highest frequency (done!)
>> 2) next,adjust the TX dial to find where the lowest frequency is 
>> shown on the dial.
>> 3) if not tracking,note where the lowest frequeny is shown on the TX 
>> dial, and move the TX dial 1.5 times the error in the opposite direction.
>> 4) adjust that new point to the lowest TX frequency with the osc coil.
>> 5) Move the TX dial to properly indicate the lowest frequency
>> 6) Use trimmer to tune to the lowest frequency.
>>
>> I reworded it to accommodate modern test procedures using a frequency 
>> counter instead of "zero beat"
>> Does this sound about right?
>>
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