SP-600 failure

[Radiomarine]

Last night I fired up the radio with a slow start as always and after a few minute's I heard a fairly loud POP! I think from the speaker . The volume and RF gain was turned all the way down as usual. . I pulled it out of the rack in hopes of finding just a bad tube, and noticed the oa2 was cold . I went through all of the tubes with the tester and only found a few 6ba6's with low emission. I'm not much of a tech ,so beyond that I imagine it's a resistor or cap . There is no audio from the rig at all . Nothing . Any Ideas ? Many thanks
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"...and the sea will grant each man new hope... his sleep brings dreams of home," Christopher Columbus.

[tinwhisker]

My schematic shows the 0A2 as V18 and is located in the power supply (not surprising). Power supplies are usually a lot easier to troubleshoot than other areas of the receiver. If your receiver has not been recapped and has black plastic capacitors, these should be held in the gravest suspicion, as these are often cracked and electrically leaky or shorted.

Check that all fuses are the correct rating, you want to protect the power transformer.

I would check for short or low resistance to ground across the filter caps, then blown fuses. Sometimes a "heavy" load, often due to bad caps, in the power supply or other parts of the receiver can load down the B+, possibly enough to not allow the 0A2 to "fire".

A schematic, variac, (or dim bulb tester) and of course a multimeter is indicated if nothing obvious or smelly is evident. (and to proceed further).

Charlie

[w3jn]

SHort in the B+ line somewhere. One recurring theme with SP-600s seems to be filter chokes that short to ground, judging from the number I've owned and seen on eBay etc with missing or replaced filter chokes.

If the 5U4is glowing red or sparking, you can bet there's a short. Otherwise the problem could be the power transformer went.

[Tube Radio]

What version of the SP-600 do you have. I have the JX-17 version with original chokes and filter caps and have had no troubles whatsoever.

Yes I would recommend replacing the tubes. Mine had a lot of the tubes reading marginal or bad on my tube tester, but the receiver still worked fairly good

[Radiomarine]

Thanks everyone for the input , It's a early one ,JX-1 US army R-274A . I took the bottom cover off and no signs of cracked caps near the OA2 , no funky smells . I'll dig around more this week . fuses ect, YEAH JOHN, THE 5U4 DID SEEM A LITTLE ON THE RED SIDE Hmmmm. Well, If I can't fix it ,the guy who sold it to me offered assistance and live about 90 miles from me . As I'd hate to ship it after seeing what happened to my last receiver . Many thanks
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"...and the sea will grant each man new hope... his sleep brings dreams of home," Christopher Columbus.

[w3jn]

You *can* fix it. You need to track down where the short is.

However there are a bazillion black beauty capacitors that need to be replaced, if they have not already been done. You'll need to pull the covers off the IF cans to get at the ones in there, and pull the RF subassembly. There are pictorials online on how to do this.

It's tedious, but not brain surgery.

[Tube Radio]

Yes replace the black beauties and also the electrolytic capacitors. On the chokes measure the resistance from one terminal to the choke's case with the wiring disconnected from the terminals. If you get low resistance the choke is shorted to the case.

[tinwhisker]

Just a reminder... If you or a friend are going to repair and later re-cap the the receiver, before lifting the R.F. Deck, PLACE THE BAND SWITCH TO A POSITION BETWEEN TWO FREQUENCY RANGES, to avoid damaging the switch contacts.

There is, or used to be, a website, where the author tells every place where there are caps to be found that need replacing.

Using disc ceramic capacitors to replace the black plastic ones, frees up a lot of space, especially in the R.F. Deck.

But first you must fix the current problem. Good luck.

Charlie

[W8ZV]

Hi There!!

Been into several of these things for customers. IF you HAVE NOT changed out the black beauties, then it MUST be done ASAP. I just got done doing that on a JX-6 that was "working". I found three that were physically split and leaking and several more that were electrically leaky. There is NO SUCH THING AS A GOOD BLACK BEAUTY cap. Use .01 and .022 ceramics as replacements. If your voltage regulator tube is not working, then you've probably blown the HV fuse in the radio. That's there to keep the supply from burning down when shorts happen in the HV section. Look there first. Check the HV line to ground (use the manual resistance references) and correct any low resistance issues you find after changing out the caps. Check any resistors that are associated with any leaky caps that you find and replace them as well. I'd only worry about tubes that show shorted on a tube tester. There is so much extra gain in this receiver that marginal tubes usually don't have a lot of effect in receiver operation. The only place that this would be as issue is in the front end of the receiver. They would generate more front end noise that a good tube will. Andy Moorer's website has a lot info on the SP-600. I will suggest that you remove a set of the RF turret coil assemblies and rotate the switch so that there is nothing engaging the bandswitch contacts. It's easy to do and you won't break any of the contacts that way. You have several of them that have to be removed to replace caps anyway, so you can kill two birds with one stone.
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Kim Herron
W8ZV
kim.herron@sbcglobal.net
616-677-3706

[Radiomarine]

I put the 600 on the back burner for now . I started working on a R-390a that need some help . It had problems in the RF chassis. Someone had added a additional gear to compensate for some kind of fault , Broken gear clamp or something . Drilled through the front panel and part of the rf deck, I even found christmas light bulbs soldered in the readout. I had accumulated a nice front panel most of a RF chassis and back panel with harness ( The back panel also had holes drilled in it. In about 3 days I have it all back together and the RF deck an xtal oscillator aligned for 7 mhz , I have a few wires on the front panel that are puzzling . One wire on the function switch didn't match it's color description (Yes ,I had to solder on a new wafer as the one on the harness was broken) Patience in a bottle is the key to this kind of stuff. One wire which should go the the TB above the dial was a different color and tracked it down to p-119 plug . It funny what some people do . Anyhow, after that's all figured out I'll set- the PTO end- points and that should do it. .While soldering all the wires and just have enough wire to reach meters ,antenna relay etc, I wonder what some do about that . eventually you would have to completely replace or extend the wire .
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"...and the sea will grant each man new hope... his sleep brings dreams of home," Christopher Columbus.

[djed]

Speaking of references to the SP-600, my link to Hammarlund Historian doesn't work any more. Anyone have a current link?
Ed W2EMN

[johnS.]

I tried the Historian too, with no luck. I used the "Wayback Machine" web archive. Seems to work, but it's from 2008. Here's the link:

http://web.archive.org/web/200 ... tpage.html

Nice article on recapping the 600, there.

John S.
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I have no political statements.