[Boatanchors] SP-600

[Al Parker]

Hi Larry, et al,
	Sounds a little like AVC problems, the audio may be distorted from 
overload, the RF & IF stages may be running wide open, or close to it. 
Does that change if you switch to manual AVC & drop back the RF gain?
	I think you've eliminated tube microphonics, with your substitutions.
	I'm just finishing up the complete job on an SP-600-JX-14 that was kept 
in an un-A/C environment for some yrs.  Of the 55+- BBOD caps that I 
removed, only 6 weren't cracked.  One had a resistance of 58 ohms, and 
had smoked the dropping resistor ahead of it (in the FCU).  I've found 2 
mica caps that were bad, one was in an IF can and was one AVC problem, 
the other was also in the AVC ckt.
	As has been mentioned by Richard, and others, the selectivity switch is 
prone to getting cruddy with lack of regular use, a drop of DeOxit on 
each wafer would be good.  The turret pins do get a bit of oxidation, 
but aren't usually much problem, as long as the turret gets some use.
	With all that in mine, it actually was working before I started into 
it.  So, these things are pretty ruggedly designed, to endure various 
"hardships".
	IIRC, there was a prod. det. mod. that used the BFO buffer tube, which 
is that one at the rear corner.  I've also seen really botched up prod. 
det. mods in them that made things really sound crappy (technical term 
there).
	I hope that's a little food for thought.
73,

Al, W8UT
www.boatanchors.org
www.hammarlund.info

"There is nothing -- absolutely nothing -- half so much
worth doing as simply messing about in boats"
Ratty, to Mole

On 8/4/2011 2:52 PM, telegrapher at q.com wrote:
> 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
> _______________________________________