[Hammarlund] Rebuilding a derelict SP-600 receiver

[Richard Knoppow]

    Sort of a late note: I absolutely agree with Roy about plate 
bending. Never, never in an SP-600. Even though the plates are 
slotted they were never meant to be bent.
    However, you can made sure the stators are aligned correctly. 
The should be exactly parallel with the rotor and the ends of the 
two sets of plates should be in line. The stators are fastened in 
with clamp screws with fiber washers. They can drift 
mechanically. The most accurate way to align them is with a 
bridge but that is difficult. They can be made parallel and 
centered using feeler gauges, one on each side of a plate. If 
they are not centered the tuning curve or "law" of the capacitor 
will be wrong resulting in the calibrations being high in some 
areas and low in others. This is a fairly easy adjustment to make 
and does no damage to the capacitor as plate bending does.

On 9/12/2020 11:31 AM, Roy Morgan wrote:
> Bill:  Comments in line below:
>
>> On Sep 12, 2020, at 1:30 PM, William Radmer <bradmer at comcast.net> wrote:
>>
>> Greetings,
>>
>> This is my first post after joining the group a few weeks ago.
> Welcome.  There is lots of experience with the SP-600 here.
>> I am
>> rebuilding an SP-600 R-274C  purchased several years ago
> Hooray - great to see another one being restored.
>
>> ..(it was full of the infamous "Bumble Bees of Death”)
> You no doubt learned that there are some inside the IF or mixer cans.
>
>> RF section requiring the most effort to remove for service.
> Sounds like “previous owner damage!”
>
>> At this point, the rebuild is almost done! 72 capacitors have now been
>> replaced …. bringing AC power up slowly on a variac  while checking the B+ voltage.
> NOTE! !!:  THE filter choke may be leaking to ground.  One suggested repair by insulating it from chassis is NOT a good idea.
>
> NOTE2!!  DO NOT “bring it up slowly on a variac”. You risk frying the transformer.  Details later.
>
>
>> If no other problems come to light,  full alignment of the receiver will
>> finish up the rebuild.
> NOTE 4!! :  DO NOT try to set linearity by bending the tuning cap plates.
>
> More later.
>
> Roy
>
> Roy Morgan
> K1LKY since 1958
> k1lky68 at gmail.com
>
>
>
>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL