[Boatanchors] SP-600

[rbethman]

Look towards the bottom!

On 8/4/2011 5:01 PM, Richard Knoppow wrote:
> ----- 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
I'll add that the turret has the wipers that do build up an oxide coating.

I did not have the top band, up through coverage of 6 meters until I 
worked the bandspread back and forth to its limits.

There was apparently some crud that I could not locate sans tearing it 
all apart.

Bob - N0DGN