[Test-Equipment] Re: HP606A linearity

[John Kolb]

I had a HRO-500 receiver once that had been knifed by the dreaded
previous owner. Well yes, he had adjusted it so it was right on on
the calibration points every 25 kHz.  However he had bent all
the adjustment tabs in a zig-zag pattern looking like saw blade
teeth, and it was 5 kHz or more off between cal points.  Took
forever to get back right.
When bending the tabs, make as smooth a line as possible.

John


At 07:52 AM 6/21/2008, you wrote:


>>    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
>_



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