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#13
November 2nd 06, 09:15 PM
posted to rec.radio.amateur.boatanchors
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SP-600 Rebuilding Experiences
"Harold" wrote in message ups.com... Richard Knoppow wrote: "K3HVG" wrote in message ... I had to change 100% of the micas from a BC-669D. Also, micas in some ART-13s have also gone bad, some near impossible to get to. I don't think many of these components were ever even dreamed of to go this long! On the other hand, my SX-28, apparently in use almost continuously since is was purchased, is still humming (no pun intended!!). Hope I can get away with not doing the RF section...? Worst B/Bs I ever saw were in a National NC-125. They looked like they just dropped out of a bag of spoiled mussels. I suspect the environment has something to do with it. For instance, the BB's in my SP-600 were pretty awful but I found one in a General Radio 1001A signal generatror that looked brand new. I replaced it on general principles but it tested good. -- --- Richard Knoppow Los Angeles, CA, USA I had a SP-600-JX-14 several years ago that came from a Western Electric monitoring station on the east coast. It came with a SPC-10 and a speaker panel. I had been on continuously for 24/7 for many, many years other than for retubing and check-ups. It had "ALL" the original black tubulars. None were split nor leaky. I used it for a couple more years then sold it. I have had twenty SP-600's pass through my hands over the years, most of those black tubulars or gray ones were leaky and/or split open. The enviroment in which it was in and either in use or sitting turned off would also make a difference. In recent years the silver micas are now showing up bad, probably due to silver migration. The avc chain on the SP-600's at this point in time should be looked at closely. Many of them are bad. YMMV I have dealt with only two SP-600's. One is probably a JX-21 but might be a JX-21(it was missing the tuning unit cover when I got it), the other is a JX-17. Both have had bad silver micas in various places. The JX-17 was out of service and in storage for several years. It was re-capped at some time in the past so I didn't have problems with the ceramics, but I had to replace about 5 silver micas in various places. The JX-21 had about 3 bad silver micas. I replaced a lot of the BB's in the 21 but have not completely recapped it except for the RF deck. I've had the 21 for some 30 years and am still workign on it on occasion. It was basically a parts receiver when I got it. The JX-17 nearly mint but nonetheless had problems. Its now quite stable and works well. BB capacitors were advertised as deluxe, high stability, parts when new and are found in a lot of high quality equipment. I first heard that they were trouble makers more than 30 years ago. Silver mica caps are supposed to be among the most stable of all but I learned long ago that they often had a stability problem resulting in a small, rapid variation of capacitance sometimes called scintillation. I have no idea of what the physical change is that causes this problem, your suggestion of migration of the silver is as good as any. Its also obvious that dipped epoxy encapsulation is far more stable than the old molded plastic (Bakelite maybe) types. BTW, the stability of the SP-600 is affected by line voltage variation due to lack of heater regulation. I have a Sola constant voltage line transformer that helps with this. -- --- Richard Knoppow Los Angeles, CA, USA |
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