[Hammarlund] PSK-31 on an SP-600

[Richard Knoppow]

----- Original Message ----- 
From: "Les Locklear" <leslocklear at cableone.net>
To: <k2cby at optonline.net>; <hammarlund at mailman.qth.net>
Sent: Sunday, August 07, 2011 4:34 PM
Subject: Re: [Hammarlund] PSK-31 on an SP-600


>I have a modified John R. Leary that has a product detector 
>and listen to ssb nets for hours on end with a couple of 
>light touches on the tuning knob.
>
> Ain't technology great? All those bells and whistles and 
> 1950's stuff still keeps pace!
>
> Way to go Miles.
>
> Les Locklear
> Gulfport, Ms.
> DX'ing Since '57
>
     The SP-600 was designed to be a very stable receiver. I 
suspect the reason many complain that they are not is 
because their receivers have problems. I think a lot of 
SP-600's work but are sick. For one thing apparently the 
stators of the tuning capacitors drift with time. They 
should be exactly centered both between the rotor blades and 
vertically. They are clamped in place so I suspect can move 
around just a little with time. This will also affect the 
dial calibration, which should be quite good, and the RF 
tracking, which should also be right on. I've found a couple 
of receivers where someone has bent the plates of the 
capacitors to try to compensate for the effect of the 
stators being out of place. Once bent they can never be 
gotten quite straight again so it should NEVER be done. 
Aligning the stators requires removing the capacitor from 
the tuning unit, not too difficult but a lot of work.
     Some of these receivers are also very microphonic. I 
think that may be where the original, rather large, paper 
caps were replaced with disc ceramics. The ceramic caps can 
vibrate. I have not yet tried a cure I think will work, 
namely fixing them in place with blobs of silicon rubber. 
Its easily removable. I have a couple of receivers on the 
back burner, may take a while to get to them but will report 
on what I find when I do them.
     Another problem is that there is no regulation for the 
filaments of the oscillator. When line voltage changes it 
can cause quite a bit of drift. My solution was just to put 
the RX on a Sola transformer. If you have reasonably stable 
line voltage this will not be a problem

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