[Test-Equipment] Re: HP606A linearity

[rbethman]

Richard & Mark,

I suggest you go to <
63k - 9 sec @ 56k
http://bama.*edebris*.com/manuals/ 
<http://wzus.ask.com/r?t=p&d=us&s=a&c=a&l=dir&o=12770&sv=0a30051f&ip=45f30f2b&id=2B27F09830D8BD3E69980211C6947C15&q=edebris&p=1&qs=145&ac=24&g=50e4DkN0r3S4p3&en=te&io=0&ep=&eo=&b=alg&bc=&br=&tp=d&ec=10&pt=http%3A%2F%2Fbama.edebris.com%2Fmanuals%2F&ex=tsrc%3Dtxtx&url=&u=http://bama.edebris.com/manuals/>> 
and go to HP.  You will find a listing FOR the 606A.

It is approximately 3.4MB PDF file.  It IS the Operation AND Service 
manual printed by HP.

You will find your answers within Section IV - para 4.9.

By the way - AT NO TIME does the service section REMOTELY mention 
"manipulating" the variable capacitor WHATSOEVER!

Bob - N0DGN


>>    I recently obtained one of these guys at a local sale. I
>>> worked for -hp- for many years and must have repaired dozens
>>> of them but its been perhaps 40 years since I've worked on
>>> one and I can't remember certain things.
>>>    This one has had plate bending done to the tuning
>>> capacitor. In particular the plates at the high frequency
>>> end have been bent to lower the capacitance. I can't
>>> remember if this was a normal factory method. Usually plate
>>> bending on any multiple band device is a no-no and I suspect
>>> the plates should be straight on this one. Does anyone know
>>> for certain?
>>
>> Bending the plates of the tuning capacitor (knifing it is usually/was 
>> called) is pretty common to reach the desired linearity.  Usually 
>> certain rotor plates are slotted to allow bending the rotor "tabs" 
>> over various ranges of the capacitor travel.
>>
>> My own 606A has a linearity issue, in that I can align the end points 
>> but the middle of every frequency range reads high.  I didn't spend 
>> much time investigating, thinking there may be a mechanical issue 
>> with the gearing but it's possible knifing the tuning cap will be 
>> necessary to bring the unit back into specs.  Not a big deal as I 
>> used a frequency counter to display the output frequency anyway.
>>
>> BTW as it is capable of 100% modulation the 606A and B make fine low 
>> power AM exciters on 160 and 75 meters. There is a bit of carrier 
>> frequency "warble" with modulation present on the 606A that gets 
>> worse with increased frequency.  This was addressed by the added 
>> buffer stage in the 606B.
>>
>> "Rig here OM is a HP606A driving a SB-220; to about 15 carrier watts 
>> output"
>>
>> Mark K9TR
>
>     I am skeptical about plate bending on multiple band devices like 
> the 606. My problem is that even though I must have worked on dozens 
> of them for -hp- I don't remember if this was done at the factory. The 
> usual technique with other generators was slipping the dial to get the 
> tuning range on the right part of the capacitor. I straightened the 
> bent plates on this one as best I could and tried the dial slipping 
> technique. So far its brought the calibration much closer. This is 
> work in progress so I don't know yet whether this will fix the 
> calibration.
>     I suggest you try this trick on your generator. The dial is held 
> by a clamp which is accessible by removing the main tuning knob. The 
> direction to move the dial depends on whether the mid-frequencies are 
> too low or too high.
>     Nearly all large variable air capacitors have slots cut in the 
> outer plates. Its very tempting to bend these plates but I know for a 
> fact that doing so will get you in trouble for some equipment, for 
> instance SP-600 receivers.
>     The high quality modulation of the 606 is one of its great virtues 
> along with constant output. Mine is about perfect other than the 
> calibration problem.

-- 
Bob - NØDGN