[Hammarlund] SP-600 HFO Alignment

[Richard Knoppow]

    On the Hewlett Packard 200CD and the 606A the plates were 
bent at the factory. The 200CD has instructions for bending them. 
I would not do it. If the plates are bent from the factory leave 
them alone. Its possible for a variable capacitor to become 
asymmetrical. This can often be fixed by adjusting the main 
bearing. Adjust it for minimum capacitance with the plates fully 
meshed. I suspect a lot of plate bending was done to fix the 
error caused by the plates not being centered. The fact that the 
outer plates have slots doe not mean they were intended to be bent.

On 3/24/2020 11:23 AM, Bill Cromwell wrote:
> Hi,
>
> I took some radio/tv classes for a while (once upon a time) and 
> they taught bending the *outer* rotor plates to get tracking in 
> the AA5 AM broadcast band receivers. I have seen radios with 
> intentionally bent plates and there was no satisfaction there. 
> Don't do it.
>
> 73,
>
> Bill  KU8H
>
> On 3/24/20 11:11 AM, k2cby at optonline.net wrote:
>> I would repeat in boldface underlined Never bend the plates of 
>> the tuning
>> capacitor! It is undoable and a death sentence so far as 
>> proper alignment is
>> concerned.
>>
>> That said, there are several points to consider in trying to 
>> match the HFO
>> frequency to the tuning dial.
>>
>> 1.    On the frequencies below 7.4 MHz (the 3 lower bands) be 
>> sure that
>> the IF is actually centered at 455 kHz, and on the higher 
>> bands be sure that
>> the IF is aligned at 3,955 kHz and the crystal oscillator is 
>> putting out
>> 3,500.00 kHz.
>> 2.    Be sure there isn't some non-factory "improvement" 
>> hanging off the
>> wire that runs from the plastic feed-through at the front of 
>> the RF strip to
>> the VFO-Crystal oscillator switch. That wire leads directly to 
>> the HF
>> oscillator, and any stray capacitance to ground will foul up 
>> the frequency
>> calibration at the high end.
>> 3.    Without touching the oscillator coils, use the proper 
>> size steel
>> screwdriver to "exercise" the air variable capacitors of the 
>> oscillator
>> section for each band. Especially if the boat anchor has been 
>> sitting
>> untouched for a couple of decades, the capacitor shafts will 
>> stiffen and you
>> will either bend or break a plastic alignment tool.
>>
>>
>> Miles B. Anderson, K2CBY
>> 16 Round Pond Lane
>> Sag Harbor, New York 11963-3821
>> Phone: (631) 725-4400
>> FAX: (631) 725-2223
>>
>> e-mail: k2cby at optimum.net
>>
>>
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>

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL