SP600-JX21 s/n 19113
as arrived, 5/30/02
Now here's the way to pack & ship one of these - an "industrial grade" computer shipping container. The package weighed 122 pounds, everything arrived in perfect condition, via FedEx 2-day Air.
progress report #1
Have spent a little time, 2 or 3 times, mostly getting acquainted.
At first it seemed extremely sensitive, overloading. The S-mtr did register high, so AGC voltage should be there, just not doing it's job in an early stage I expect. Audio output was low, so I put an external amp on the diode load terminals, and it was fine that far. So there's another thing to look into, the audio stages. I hope it's not the output xfmr, I know of several that have gone bad. Overall sensitivity dropped drasticly this PM after being on for abt an hr, but I was also messing with my ant. tuner since I had just put up a new outside wire for use in the shop. (I've found that a tuner does great things on a rcvr when you are band cruising.) Don't know yet if it was my problem or what.
The BFO seems weak, and quite a bit off the IF freq. IF freq. will get set to the xtal filter freq. b4 doing IF alignment & BFO zero. IF freq. may end off a bit away from 455.0, but it needs to be on the xtal so selectivity positions don't drop the level independently (now they do).
The knobs should clean up real fine. Most of their problem is a buildup of crud, probably nicotine, which is also quite visible on the panel around the xtal freq. ctrls. It scraped off the knobs with my fingernail, so a soak in dishwashing soap will do most of the work.
I have not done any checking electrically, next session I'll pull & test tubes to see if they may solve the 2 noted problems, then get checking socket pin resistances to gnd vs the manual. I've not found much problem with resistors in the SP-600's, but this ck will rule out that & the disc caps.
progress report #2
As we both said, the sensitivity seemed intermittent.
I ckd all tubes, found that the 1st audio had a 12AT7 instead of 12AU7, will
work, but low gain, so chgd it. Also found that V-14, 6AL5, AVC amp, was
intermittent in the tester. It was dropping completely out, so AVC wasn't
there & all ctrld stages ran at max gain when it wasn't operating.
That made it seem super sensitive, and distorted, and probably the reason the
BFO seemed weak.
All other tubes were OK
I was worried abt the audio output being very low. It wasn't that tube, at least not all of it, it was my mistake in hooking up my 600:8 ohm audio matching xfmr to the spkr backwards. In the process, I confirmed that the output xfmr is OK.
I changed the pri. tap on the power xfmr from 117v to 130v. If you have low AC line voltage, it's not necessary, but most of the country has high, 120-125, so changing that tap keeps the B+ voltage down to a better value, vs the high value it is if AC input is high.
I did a quick peak-up on the RF stages just to see if overall output would improve, but it stayed low on the S-mtr, even tho' it seemed to be fairly sensitive - just low overall gain. Figured it might be IF being off.
Pulled the bottom cover off the turret for general inspection & future cleaning. Looks good, tho' some black dusty stuff on most of the ceramic coil mounts, it brushed right off. I will clean all contacts, the black stuff probably was flaked off oxidation. There are many dozen contacts in total, but it's nice to have them all clean & smooth.
Made all under-chassis resistance checks (haven't gone to the tubes yet), it gets the AVC ckt & lots of other stuff underneath. Had a cupla questions there, but resolved it all, once I looked at a cupla different schematics. As we knew, this is a fairly late model, matches pretty well, if not exactly, to the R-274-C mil. version.
I again saw some intermittent opn, in the AVC voltage. I'll be watching that, as it came back OK. It was from the bias rectifier, not the AVC rectifier. (maybe another bad 6AL5?)
Aligned the 455 & 3955kc IF secns, made a big difference in overall gain. Now I can hear lots of stns on the AM BC band, like you should with an SP-600 -- one every 10kc, maybe weak, but there. Listened in on the MM net on 14.300 a while, I think stability will increase when I get the tuning cap wipers cleaned, etc, and it'll be easier listening with the SPC-10 :-)
The 455kc IF sections were off - on the 13kc selectivity it peaked at 450.1, the 8kc was at 452.3, 3kc at 456. The "real" freq., that the xtal filter is at, turned out to be between 455.0 & 455.1, so that's where it all is now. BFO was tweaked onto freq.
Cupla questions, it has 2 mods by an owner - a 4 terminal strip on the back skirt, which has terminals for the low impedance audio (earphone jack), and 2 of the terminals for use of an external stdby switch, e.g if you wanted to silence it from an xmtr. I thought I had noted something else, but don't see it in my notes right now.
I'll be getting into cosmetics next probably. Will take the front panel off to get it clean, and the gear train, etc, behind it. I will get everything clean, & will shine it up some, or lots.
I'll redo the alignment after all else is done, plus I haven't done the RF secn to peak it up & get the dial freq. on. It's off abt 150kc on 14mc, abt 100kc on lower bands. It'll never be a freq. meter, but should be very close to the best you can tell with the dial pointer.
progress report #3
I have spent several hours removing the panel, partially
cleaning it, and cleaning and waxing the knobs, which now look very good.
The panel will require some more attn, the nicotine stains were very thick
in several areas, and the lettering will require some touchup, but overall it is
& will be quite nice. I've mixed some matching gray paint to fill some
nicks, etc. The date on the back of the panel is May 15, 1955.
The gear train area is fairly clean, some small pitting in areas (not on the gears), the gearing is good, will need some cleanup to remove old caked lubricant. The chassis in general will be cleaned, side panels may be removed to make that easier. (pix b4 cleaning) (hawk not related)
after cleaning the nicotine stains, etc. Area of Freq. Ctrl was very thickly stained, note paint erosion at lettering edges.
Filling letters, 2 or 3 times in some areas. Artist's acrylic paint.
in process of cleaning up the acrylic.
Complete - still can notice some staining which will be underneath knobs. Sorry some pix are a little fuzzy, and the color isn't really so dark.
Now on to the chassis cleaning and panel replacement.
paint bezels, clean chassis
These were wet sanded, primed, wet sanded & finish coated with
Hard to really see well due to "bright black" in sunlight.
Still wet, will dry quickly in the 90F+ sun. Only brushed with soap
& water, rinsed with distilled water.
IF cans were buffed yesterday, now back into the A/C for re-assembly. Will put light coat of light mineral oil, cut with naphtha, on chassis, to retard any aluminum oxidation.
Cupla days off last week, little time off for a diversion, spent the nite in Oriental, about 20 mi. down river:
Broad reach, 15-20kt wind, xyl, Pat, at the helm. Oriental, NC, harbor, with shrimpers.
Back to work -- more cleaning & reassembly, pix w/ & w/o flash to show slightly different coloring.
Spent a lot of time cleaning pieces as they go in, like wire brushing screw heads, cleaning and DeOxiting tube pins & turret pins. This is the fun time - seeing it go back together, doing the final alignment, and hearing the sensitivity improve as things come in. Got the new electrolytics in the power supply, checked about 6 tube socket pin resistances, all close to expected value. Still a few kinks to straighten out, the 7 - 14 mc band has an intermittent, which seems to be in the antenna section in the turret. Will pull that module out and take a close look. It seems as sensitive on 50mc as at 1mc, and it's great at 1, - I can hear a BC stn almost every 10kc. I listened to the MM net on 14.300 SSB for half an hour this PM, without the converter, which I'll get into soon.
The SPC-10, a neat unit, too bad they aren't more common.
I brushed the dust out, and washed the covers. Then set the 455kc IF to match the SP-600's, at 456.2, and peaked the 50kc IF. This makes listening to SSB signals a piece of cake on the SP-600, no more need to ride the AVC when tuning between signals.
New filter caps & 3-wire line cord.
I rewired the AC input to put the hot line to the switch, the neutral line to the input voltage tap on the transformer, and replaced the line filter caps with .0l @250vac discs.
I think this one's just about complete. I've enjoyed band cruising with it, tuned in CHWO, 740kc, in Toronto Thurs. nite to listen to their big band nite, and found WSAI, 1530kc, in Cincinnati, but they weren't playing oldies Fri.
Ready to pack up
I've made cables for connecting the 2 units, and a pwr cord for
the SPC-10, and a cable to go from the diode load terminals to an external audio
amp. All connections shown in the pix below.
While listening this afternoon, I didn't like the short term frequency stability on the 7-14mc band. It "warbled." I determined that the HF oscillator module for that band, in the turret, was causing it. It has 2 mica & 1 temp. compensating capacitors in it, apparently one is bad. I swapped in a module from another receiver that works fine. Someday I'll come across proper values and repair the bad module.
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This page last updated on 03/20/2005