[Test-Equipment] HP-606A Calibration question

[Richard Knoppow]

----- Original Message ----- 
From: "Barry" <n4buq at knology.net>
To: "Discussion of Electronic Test Equipment" 
<test-equipment at mailman.qth.net>
Sent: Wednesday, May 27, 2009 5:24 AM
Subject: Re: [Test-Equipment] HP-606A Calibration question


>
>> No, there is a unique solution, not multiple 
>> possibilities.  This can
>> be verified
>> by using a resonance calculator such as
>> http://www.daycounter.com/Calculators/LC-Resonance-Calculator.phtml
>> and entering some different values.
>
> I should have realized that.  I was thinking there was a 
> random variable
> involved in this that would let the L and C "move" and 
> stay in resonance,
> but that's not the case.  At any given position on the 
> dial (and hence the
> variable cap), the other "variables" are fixed so the L 
> and C must be
> specific values for resonance.  Thanks for straightening 
> me out on that one.
> I guess I was just grabbing at straws trying to arrive at 
> a reason why this
> thing is so far off calibration at it interior markings.
>
>>
>> John
>> KK6IL
>
> Barry - N4BUQ

     This is being made more complicated than necessary. 
There only a couple of things that will cause the tuning 
"law" to be far off. One is that the dial is in the wrong 
place, the other is that the tuning capacitor is damaged in 
some way. Examine it carefully to be sure the stators are 
parallel with the rotor and evenly spaced. If they are then 
adjusting the dial should bring it in. As I described before 
there are now three adjustments: 1, the L; 2, the C;, 3, the 
dial position. These three must be juggled to bring the dial 
in. Set the L and C for the band ends, check the dial at 
intervals along the band to find where the error is 
greatest. Slip the dial a little one way or the other and do 
the L and C again. Then check the center range to see if you 
made the error larger or smaller. If smaller then continue 
to slip the dial in the same direction, if larger slip it 
the other way. Keep slipping it incrementally and then 
resetting the band ends. Unless the cap is damaged you 
should be able to bring the dial in very closely all over. 
When you have done one band clamp the dial firmly. The other 
bands should also be in when the L and C are adjusted at the 
band ends. This really only needs to be done once.
     To those suggesting looking for set screw marks there 
are none on a 606A or B. The dial is clamped to the shaft by 
a ring with longitudinal screws and there are no marks.
     The dials for the 606A/B are not individually 
calibrated so even if someone changed the dial it should 
still come into specs.
     I have no idea how a dial could be moved but its pretty 
easy and a lot of people work on this stuff who, bluntly, 
don't know what they are doing.
     Using a counter to set the frequencies makes the job a 
lot simpler than trying to use a crystal calibrator.
     If, after doing the calibration procedure carefully the 
thing stils won't come in the trouble is likely the tuning 
caps. They are hard to see when the generator is assembled. 
If you have this problem write and I will describe how to 
get at the caps. Its a lot easier than it looks.


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