sp-600 J drift

[ve8xj]

Hello again

   First off thanks to the last bunch who helped me with great info regarding the sx-28 and bc-610h.

I just finished a total recapp on the Sp-600 I've had for about 20 years ,which was much needed.The old set has sprung back to life. I have been comparing it to my r-390a for fun and surprised how well it holds up in some regards. It certainly has a lower noise floor,and nicer audio.But unfortunately there is much more drift than I would like. I have to touch up the tuning every minute when on sideband.Thats about as bad as my S-20R ! Pretty significant for a top of the line communications receiver.,and I'm guessing way out of spec.Does anyone have any thoughts? I realize that I will not get the performance of a R-390a from this Sp-600J. Even though I have heard people compare it as a equal That could be true of the jx-21 or some of the later models but not a J serial #1037.BUt I no doubt should get the drift under control.I am however no where near a electronics tech as some of you.
Now I did replace some resistors I did not replace many though just those that were suspect.I will someday replace all of them but the goal this time was to get it up and running again.
At first I thought gear backlash but not so in the end.

Cheers Ve8xj

[N8ETQ]

    I wonder how much warm up time it had?  It may settle down
a bit in a day or so.  Slop bucket could be BFO pulling.  Zero beat it to
an AM carrier, If its drifting you'll hear it.  Of course if your doing this
above 20 mc or so all bets are off.

   GL

/Dan

[ve8xj]

    I wonder how much warm up time it had?  It may settle down
a bit in a day or so.  Slop bucket could be BFO pulling.  Zero beat it to
an AM carrier, If its drifting you'll hear it.  Of course if your doing this
above 20 mc or so all bets are off.

   GL

/Dan

Yes thats true the warm up time is significant ,and I do hear the drift after about 12 hours of warm up. I do not have a cabinet for it though and it doesn't get as warm as it should ,but can't imagine that would make too much difference but I could be wrong.

What do you mean by BFO pulling?

Yes , I agree anything over 20mc is a write off.

[Todd, KA1KAQ]

Sounds like a perfect description of power line drift. Check your transformer taps, see where the line is connected. Most likely it's on 115volts. If so, move it up to 125 or whatever the next highest terminal is(it might be 120 to 130 instead of 115 to 125). Been a while since I had mine upside down, but I'm pretty sure those are the values/taps. AC line levels have risen somewhat since these rigs were made, 110-117 quite often is now 120-125 or higher. When you exceed or even start bumping up against the 115 terminal limit the receiver will wander all over as the line voltage rises and sags.

Had this issue with mine and as soon as I moved the tap up, the crazy drift went away and only typical warm up drift remained.

[N8ETQ]

KA1KAQ said

"Sounds like a perfect description of power line drift."

  Good point,

/Dan

[ve8xj]

Sounds like a perfect description of power line drift. Check your transformer taps, see where the line is connected. Most likely it's on 115volts. If so, move it up to 125 or whatever the next highest terminal is(it might be 120 to 130 instead of 115 to 125). Been a while since I had mine upside down, but I'm pretty sure those are the values/taps. AC line levels have risen somewhat since these rigs were made, 110-117 quite often is now 120-125 or higher. When you exceed or even start bumping up against the 115 terminal limit the receiver will wander all over as the line voltage rises and sags.

Had this issue with mine and as soon as I moved the tap up, the crazy drift went away and only typical warm up drift remained.

Thanks ,that is a very good point . MY line voltage is generally 127vac and we use generator power when they are having problems at the dam. My transformer and chokes are running a little hotter than I would like. I will give it a try when my bench is clear.

I will let you know. For now I have put a variac in front of it to observe.

Cheers

Tim

[k4kyv]

All the Hammarlund Super-Pro series, including the SP-600, have a notorious reputation for frequency drift. Inherent to the design of the tuning capacitor.  Better to use it for AM reception with the diode detector, and use something like a R-390 or 75A series for CW and  SSB.

[iw5ci]

Well i have a collins 390, and a couple of sp-600, one of them jx-29.
I Also have an hammarlund 180ac. Well, while the 390 gas an incredibile freq stability even from cold, while the 180 have to stay on for almost half an hour to be usen on ssb, both sp-600 Are stable after 10 min warmup. After 10 min i need no more to move the freq control for all day. My sp's work at 220v. So i think that your receiver have some problems and you must fix it. Which type of condensers you used for recapping?!

[Todd, KA1KAQ]

All the Hammarlund Super-Pro series, including the SP-600, have a notorious reputation for frequency drift.

That's not entirely true, Don. Or, at least - the drift part isn't. There were plenty of stories for sure, and I believed much of it myself until I started doing some research. Part of the issue with the early Pros was the amount of time it took for them to stabilize, and the manual even covers proper usage including leaving the radio on 24/7. SP-600s suffer from bad caps and the notorious improper tap selection. I was amazed at how stable my 600 became when I changed the transformer tap.

Henry Rogers has an excellent dissertation on his site explaining many of the problems and misconceptions around the 200 series. Well worth reading.

http://www.radioblvd.com/hammarlund_super_pro.htm

Under "Expected Super Pro Performance:

".....It is unfortunate that these incredible receivers have had to endure endless deriding from hams and SWLs over the past several decades. The low opinion of the Super-Pro probably originated from hams and SWLs who, in the 1960s, happened to obtain a well-used surplus BC-779 receiver (that like most Super-Pros was still operational) and began using it right away without doing anything to the receiver......"

There's more under "Modification Mayhem" explaining what lead to so much bad press, Basically, trying to turn an old receiver into a new receiver capable of receiving SSB. You're dead on the money there, Don - the Super Pros will work, but there are far better choices. They are excellent for AM.

And there's one simple mod to add a temperature-compensating cap which was published some years ago, makes a huge difference in warm up drift.

[WZ1M]

As I mentioned in another thread, I have done several SP-600,s. Not Just your quick cap job but to the point where you would not know what it was from the parts laying on the bench. My favorite SP-600 is my JX-1. Spent alot of time on this including restoring the front panel. I found that drift was due to mechanical issues, not electrical. These receivers were used alot and the feed tru bushings for the main tune shaft have wore to an oblong shape. Easy to check, just grab the knob and see if the shaft is loose in the bushing. What I see is the shaft riding up on the old grease in the busing and from the weight of the flywheel starts to settle down into the worn part of the bushing. This causes the tune cap to move slightly and thus the drift. New bushings fixed the problem almost every time.
Regards,
Gary

[ve8xj]

Well i have a collins 390, and a couple of sp-600, one of them jx-29.
I Also have an hammarlund 180ac. Well, while the 390 gas an incredibile freq stability even from cold, while the 180 have to stay on for almost half an hour to be usen on ssb, both sp-600 Are stable after 10 min warmup. After 10 min i need no more to move the freq control for all day. My sp's work at 220v. So i think that your receiver have some problems and you must fix it. Which type of condensers you used for recapping?!

 Well I did in the end turn over the old girl and change taps now I just have to let it warm up.
I used .01 orange dip caps at 630v to do the job.

I certainly as I said do not expect the stability of the 390 ,and mostly operate AM but it would be nice to listen to ssb while I putter on the bench without having to come back to the bench every 20 seconds. Perhaps There's hope though.

[ke7trp]

Do you have the correct four lamps in place?  They are on the Fil line. 6 volts AC.  Start by checking the fil voltage on your line.  Mine was 7.5!!   I had to use a Small Variac to lower this back down to the factory setting.  

I have the AADE digital display for the 600.  This replaces the osc tube shield and gets its power from aligator clip leads to Lamp power and ground. This way, You dont have to modify the radio and you get a nice back lit display. Using this as a Reference:

Receiver on 5 hours at set to 3870 exactly.  Turned RXer OFF and went to bed. Just turned it back on.

Instant:  3873.1
10 seconds: 3870.5
5 minutes: 3870.2
10 minutes: 3870.0

So in 10 minutes mine is back to 3870 exactly.

I have four SP600s.  They are rock solid stable. I can run a night of radio and never once touch the tuning.  I have listened to SSB on them as well and needed no touchup but I have only done this on one of them.  

In short, I think something is wrong, Your line voltage might be way to high, The radio is not in the case, or the lamps are unplugged or burnt out. Its also possible that one of the tubes is the culprit.

I ran Blue LEDs in mine for a month and realized that the radio was not as happy or stable. I put brand new surplus GE bulbs back in the radio and its just rock solid.

I have a Collins built R390 and a Collins built R390A. I dont like them near as much as the Sp600.  Its not for the audio reasons, I feed outboard tube amps called  "voice of music" for HIfi.  These amps use a single 6bq5 for output. I just like the look of the Sp600 and the tuning. They are as stable as the R390s as far as I have seen.  My only complaint is that going from 75 to 40 meters is many dial turns.  I put in all the popular AM Freqs in the Xtal sockets and now just flip the Xtal switch.

C

[KM1H]

Todd, the old Pros drifted bad right out of the crate.

Read the WW2 QST's and you will come across the 24/7 hint as the only solution. Some AAF users had a multi position crystal controlled oscillator module developed which the SP-600 obviously copied

The boys at Bletchley Park also evaluated the "great drifter" and went with HRO's.

Carl

[KE5YTV]

Clark, I'm with you. My SP600 is rock stable  It came without the BBOD's. After a 5 minute warmup it will stay on frequency for days. I love mine, and intend to add a digital display soon.

Mike

[ke7trp]

Yep. Its still on from that test. Reads the same. Has not moved 1KC all day.  Mine does not have any BBods in it. Never did.  One of them does have them and one did have them. I would have to test that to confirm that some models Drifted and some dont. 

The display is really neat Mike.  The guy is helpfull. The webpage is confusing.  You need the tube shield KIT. You can build it in 10 minutes.  I ordred my display box built. It sits ontop of the SP600 and I programed it to say "SP-600 3870.00"  You can set it to lots of different radios.

C

[ve8xj]

Do you have the correct four lamps in place?  They are on the Fil line. 6 volts AC.  Start by checking the fil voltage on your line.  Mine was 7.5!!   I had to use a Small Variac to lower this back down to the factory setting.  

I have the AADE digital display for the 600.  This replaces the osc tube shield and gets its power from aligator clip leads to Lamp power and ground. This way, You dont have to modify the radio and you get a nice back lit display. Using this as a Reference:

Receiver on 5 hours at set to 3870 exactly.  Turned RXer OFF and went to bed. Just turned it back on.

Instant:  3873.1
10 seconds: 3870.5
5 minutes: 3870.2
10 minutes: 3870.0

So in 10 minutes mine is back to 3870 exactly.

I have four SP600s.  They are rock solid stable. I can run a night of radio and never once touch the tuning.  I have listened to SSB on them as well and needed no touchup but I have only done this on one of them.  

In short, I think something is wrong, Your line voltage might be way to high, The radio is not in the case, or the lamps are unplugged or burnt out. Its also possible that one of the tubes is the culprit.

I ran Blue LEDs in mine for a month and realized that the radio was not as happy or stable. I put brand new surplus GE bulbs back in the radio and its just rock solid.

I have a Collins built R390 and a Collins built R390A. I dont like them near as much as the Sp600.  Its not for the audio reasons, I feed outboard tube amps called  "voice of music" for HIfi.  These amps use a single 6bq5 for output. I just like the look of the Sp600 and the tuning. They are as stable as the R390s as far as I have seen.  My only complaint is that going from 75 to 40 meters is many dial turns.  I put in all the popular AM Freqs in the Xtal sockets and now just flip the Xtal switch.

C

Thanks for the response
  Yes I have all four lights in . Love the blue lights in yours ,very jazzy!
I have managed to get the drift somewhat under control but have yet to eliminate it.

I have so far changed taps on the transformer and played with the bushings on the tuning shaft. Both with moderate success.But no where near as to what you are saying can be acheived.  If there was any chance that I could get the old gal as stable as the 390 then one day I will have to give it a try. As for now it is back in the rack doing its job moderatly well . Until the day it is back on the bench I have a AR-88 and 2 CR-88s to totally restore and get functional.

All in all been very pleased with the funtion of the Sp-600J,In fact I'm tuning around a very dead 80m , I think it could definitly use one of the those fancy frequency displays  ,Just so one knows at all times where they are though. I like the fact that it is non invasive.

I wish the bands were stable enough for a full time am frequency to actually talk about this stuff instead of all this infernal typing.

Listen for me on evenings on 20m.

Ve8xj

[ke7trp]

Something is wrong with yours. Start by checking the voltages and then go through the tubes.  The guys here can give you more indepth service plan.

C