[Boatanchors] SP-600

[Richard Knoppow]

----- Original Message ----- 
From: <telegrapher at q.com>
To: <boatanchors at mailman.qth.net>
Sent: Thursday, August 04, 2011 11:52 AM
Subject: [Boatanchors] SP-600


> My sp-600 started going south a few days abck.  Noticed 
> some ringin when i moved the tuning dial across the band 
> rapidly.  I could hear what sounded like oscillations and 
> ringing from the speaker.  I found that if i smacked the 
> main tuning dial it would quit.  hmmm.  Need a bigger 
> hammer maybe.  then last night the audio got really 
> scratchy and sounded like it was off frequency.  This AM i 
> went thru it and replace about 7 tubes that failed to meet 
> specs.  Been a while since that has been done evidently. 
> Now while the meter reads about the same, audio sounds 
> like they are using VOX to talk with even on SW stations. 
> And it's still a bit scratchy even though signals are nice 
> and loud.
>
> I did not have 6BE6 tubes so used 5915 types instead.  One 
> thing if ound is that in the back left corner (viewed from 
> the front) the 6BA6 marked on the chassis is a 6AH6 in the 
> socket.  The 12AU7 has a 12AT7 in it's place.  I tried the 
> original chassis marked tubes but that didn't work so now 
> i have new 6AH6 and 12AT7 tubes in those sockets.  I think 
> they are there because of the radio having been modified 
> for SSb receiption.  Does anyone know if that would have 
> been done for a mod like this?
>
> All tubes now in the radio test well above minimum levels 
> according to the tube tester charts.  Only thing i can 
> think of that may have caused this were the two 6BE6 tubes 
> and maybe the 5915 types, while the test settings are the 
> same, may indeed not be valid subs.
>
> I need some good 5750/6BE6 types.  Or even the GE 5Star 
> rated 6BE6 would be nice.  I've pulled some supposedly new 
> RCA types and found that they wouldn't even meet specs. 
> Same with 5750's from JAN stock.
>
> Comments?
>
> Larry
> W0OGH

     First, what instruments do you have available to you? I 
can suggest further trouble shooting but you will need a 
good voltmeter and a scope will help. Note that the voltage 
charts for the SP-600-JX were written for a 1000 ohm/volt 
meter, most modern meters are 20,000 ohms/volt and will read 
high in some places. The exception is where grid voltages 
are specified, these are to be measured with an 11 megohm 
electronic voltmeter.
     Since the problem appears to go away with mechanical 
shock I am suspicious of a cold solder joint somewhere. You 
may be able to find it by poking at the circuitry with an 
insulated stick (a wooden coffee stirrer works OK).  Also, 
does working the band switch have any effect?
     When the problem happens also try rapping on the 
various IF cans and on the tuning unit cover.
     Also, does it change when working the bandwidth switch? 
How about the fixed frequency crystal/VFO switch?
     While a bad capacitor can cause a similar symptom it 
would be continuous and not respond to banging on the panel.
     If you can get the problem to persist you may be able 
to find it by simple signal tracing if you have a good 
scope. While a somewhat elaborate receiver the SP-600 is 
really quite straight forward.
     Very extensive documentation is available from many 
sources on the web. There are few differences from model to 
model, the greatest differences being in the JX-17, the one 
with the red knobs on the front, and those are mostly in the 
BFO and fixed frequency oscillator.
     I suggest getting one or more manual versions printed 
and bound and have the schematics printed large so you can 
trace around on them.
     These are very good receivers but I think many of them 
are sick even though they seem to work OK.


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