SP-600 Rebuilding Experiences
Richard,
I performed an electrical restoration on an SP-600 (JX-26) last summer. The frequency accuracy was poor....WWV at 10 MHz was at 10.2 MHz (approx). What is worse IMO is the tracking across the bands. The frequency at one end would be high, but at the other extreme, it'd be low. I'm sure this can be tuned out. I just haven't tried yet. I'm in the process of bring back another JX-26 now, so if you have any specific questions, you can write me off list. Steve W6SSP |
SP-600 Rebuilding Experiences
Well, let's see... I've done four of them, to date. Maybe I've been
lucky or something, but I haven't had too much of a problem aligning the dials. Perhaps my spec is not tight enough? At any rate, two of the four had tubular, vice disc, capacitors that had to be changed out. The worst problem, but doable, are those on each of the L/C elements in the turret and those under the RF box. Replacing the caps on the L/C elements for the LO may be of great help in dial alignment. |
SP-600 Rebuilding Experiences
"K3HVG" wrote in message ... Well, let's see... I've done four of them, to date. Maybe I've been lucky or something, but I haven't had too much of a problem aligning the dials. Perhaps my spec is not tight enough? At any rate, two of the four had tubular, vice disc, capacitors that had to be changed out. The worst problem, but doable, are those on each of the L/C elements in the turret and those under the RF box. Replacing the caps on the L/C elements for the LO may be of great help in dial alignment. My JX-17 had bad caps on the 7.5mc to 14.5mc oscillator assembly. The problem was extreme instability. I replaced the bad guy. Since this was a 1% cap of specified value I built one of the right value from two dipped silver micas in parallel, measuring it on a bridge. The result was just about perfect calibration on that band and very good stability. I may have to change others. I am aware of he problem with the Sangamo "Black Beauty" caps. they were all replaced with disc ceramics in my JX-17 but only in the RF deck of the JX-21, or perhaps its a JX-26. I've replace a number of them that were obviously bad but there nearly 60 in the receiver and not all are bad. BTW, these ubicutous caps were originaly marketed by Sangamo as deluxe quality replacements for wax dipped paper caps. They are paper impregnated with Mylar in molded resin cases. I suspect the problem is that the casing is not stable and, as it drys out, disturbs the connection of the capacitor to the leads and also lets moisture in causing very high leakage. Black Beauties were used in a variety of high quality electronic equipment c.1950s and 1960s. Sangamo also sold dipped epoxy encapsulated versions of these sold as "Chocklate Drops". AFAIK, these have proven to be a lot more reliable. But back to the calibration problem: I discovred that molded silvered mica capacitors, once considered to be most reliable of all, evidently suffer from a similar problem, i.e., they become unstable with age. One symptom is a rapid variation of capacitance sometimes called "scintillation" and that they can change value radically. For instance, the 51uuf caps used to resonate L-34, one of the 4 mhz IF coils, will change as the receiver heats up throwing off the tuning of this stage. I changed this cap in both of my receivers. I found other bad guys in the JX-17 in various places, all molded silver mica types. The main tuning capacitor of the SP-600 has stators which are fastened to the frame with three screws. The stators can move up and down and also sideways to some degree. The should be exactly centered but the up and down movement was evidently used in manufacture to adust the exact value of each section to the nominal value. I am about to try this on one of the receivers where I need to remove the RF deck anyway. The outside plates of the rotor sections are split but evidently plate bending was NEVER done and should not be done to calibrate the things. Somewhere, someone probably has the factory procedures but they do not appear to be on the web anywhere. I have a lot of other unanswered questions about these receivers. So far, even after just a couple of hours I've found at least some of what I want in this news group, for which I thank everyone. I should add that my JX-21 (or maybe JX-26) was bought as junk at C&H Surplus some 30 years ago. It was very cheap because it had wires sticking out of it. Someone had evidently begun to modify it to a JX-17. I removed the partial modifications and restored the original circuits. I then did a very large number of small repairs. The RX was missing the top cover for the capacitor compartment (I've just recently aquired one) the shield for the crystal switch (I made one but would like an original) and a couple of knobs, the RF Gain knob and one of the small Xtal control knobs. I found knobs enough like the originals to work. Recently the main filter capacitor gave out and I decided to really bring the thing to life along with replacing the cap. I couldn't find an exact replacement but did find one of the correct physical size but slightly greater capacitance (not a problem :-) ) but discovered some additional problem in the coarse of doing this. The JX-17 was aquired in nearly mint condition many years ago but was in storage for a long time. That one has come back to life very well. I get very frustrated by my lack of time to work on these guys and the difficulty of obtaining parts even here in the big city. I have gotten a liberal education about sources in the last few months. Perhaps I've just gotten old but I am a bit shocked at the ignorance of younger people about component level electronics. Oh, well, enough grousing. -- --- Richard Knoppow Los Angeles, CA, USA |
SP-600 Rebuilding Experiences
"Richard Knoppow" wrote in message ink.net... [snip] I am aware of he problem with the Sangamo "Black Beauty" caps. they were all replaced with disc ceramics in my JX-17 but only in the RF deck of the JX-21, or perhaps its a JX-26. I've replace a number of them that were obviously bad but there nearly 60 in the receiver and not all are bad. BTW, these ubicutous caps were originaly marketed by Sangamo as deluxe quality replacements for wax dipped paper caps. They are paper impregnated with Mylar in molded resin cases. I suspect the problem is that the casing is not stable and, as it drys out, disturbs the connection of the capacitor to the leads and also lets moisture in causing very high leakage. [snip] If your capacitors are anything like the oil-filled Sprague Black Beauties, I'd replace all of them on sight. It might just be my bad luck, but the oil-filled Black Beauties seem to short even harder than the wax paper caps. However, if the later paper-mylar Black Beauties are like the early series of paper-mylar Orange Drops, they should hold up well. I think the all the oil-filled Black Beauties had one of the wires soldered into a ferrule and the paper-mylar Black Beauties had both of the leads come out in the standard way. The paper-mylar Black Beauties seem much less common than the older oil filled Black Beauties. As far as I know, paper-mylar was around only in the late 50s to the late 60s. Frank Dresser |
SP-600 Rebuilding Experiences
I'll second what Frank suggests about replacing ALL of the black
beauty caps. I'm doing that now on the SP-600 I'm restoring. While none were a dead short, most showed some leakage, about 100K ohms. In many circuits, that won't cause a problem but in some its a big deal. About 1/3 had cracked cases. Steve |
SP-600 Rebuilding Experiences
Steve wrote:
I'll second what Frank suggests about replacing ALL of the black beauty caps. I'm doing that now on the SP-600 I'm restoring. While none were a dead short, most showed some leakage, about 100K ohms. In many circuits, that won't cause a problem but in some its a big deal. About 1/3 had cracked cases. Steve Two things make the Sprague Black Beauty caps a problem, and both relate to their losing oil. The cap is molded out of a black plastic, with a small brass filler tube on the banded end. The capacitors were filled with mineral oil through this tube, and the lead was placed in the hole, and crimped. They then sealed the capacitor by adding a little bit of solder. So far, so good. Well, when the capacitors are installed, very often the banded lead is close to the lug that is being soldered, and it will carry the heat to the solder seal, and to the oil in the cap. The slight pressure increase in the cap will softly blow the solder out of the seal joint, and the oil will begin to seep out of the capacitor. Note: the oil is the dielectric, not the paper. Also, most all plastics will shrink over time, and the plastic the Black Beauties are made from is no exception. When it shrinks, the leads, and the filler tube do not, and you get a small crack, and a leak. If the oil is allowed to seep out, and the moisture is allowed to seep in, the capacitor will be compromised and become leaky. Also, without the oil, the WV of the capacitor is lowered, because the oil is the dielectric. Capacitors that are used near their WV will often arc over, and become shorted.... with catastrophic results for the rest of the circuit. -Chuck |
SP-600 Rebuilding Experiences
Steve wrote: I'll second what Frank suggests about replacing ALL of the black beauty caps. I'm doing that now on the SP-600 I'm restoring. While none were a dead short, most showed some leakage, about 100K ohms. In many circuits, that won't cause a problem but in some its a big deal. About 1/3 had cracked cases. Steve Ditto on the Black Beauties, especially the ones with the little brass tube, they seem to leak like crazy. More on the average than wax capacitors many decades older. Also bad news are those pea-green molded caps with the color bands. Many Trans-Oceanics have around two dozen of those, all leaky. I havent seen any major problem with postage-stamp or dipped silver-micas, maybe it was just one manufacturer's kind that is getting flaky? There is the problem of the silver migrating on silver-micas with considerable DC voltage across them. |
SP-600 Rebuilding Experiences
Ancient_Hacker wrote:
Also bad news are those pea-green molded caps with the color bands. Many Trans-Oceanics have around two dozen of those, all leaky. I havent seen any major problem with postage-stamp or dipped There is one variety of capacitor that looks like the silver mica "postage stamp" type of capacitor with all of the dots, but isn't a mica at all. It is just a paper capacitor. They are usually dark brown in color, and fail at about the same rate as normal wax/paper capacitors. -Chuck |
SP-600 Rebuilding Experiences
Black Beauties,
I'd replace all of them on sight. Kill 'em all. They are junk by now, just like earlier wax/paper caps, for any serious application. It takes less time to simply replace one than it does to pull it out, test it, and either re-install it or replace it. You won't regret it, and you have nothing to lose. Unless you're one of those vintage electric guitar nitwits who wants to find an original "bumblebee" cap or two to provide that tasty "period" sound (i.e., distortion resulting from badly leaking capacitors, which certainly wasn't what the guitar sounded like when new). Regards, Phil Nelson Phil's Old Radios http://antiqueradio.org/index.html |
SP-600 Rebuilding Experiences
Don't let the "mica" caps fool ya. I chased an AGC problem for two days
before I found a bad "mica" buried in an IF can. That was the straw that broke the camels back. I then replaced ALL micas along with every bumble bee, which, by the way, were all cracked. -- Regards, Gary...WZ1M "Chuck Harris" wrote in message ... Ancient_Hacker wrote: Also bad news are those pea-green molded caps with the color bands. Many Trans-Oceanics have around two dozen of those, all leaky. I havent seen any major problem with postage-stamp or dipped There is one variety of capacitor that looks like the silver mica "postage stamp" type of capacitor with all of the dots, but isn't a mica at all. It is just a paper capacitor. They are usually dark brown in color, and fail at about the same rate as normal wax/paper capacitors. -Chuck |
SP-600 Rebuilding Experiences
gkb wrote: Don't let the "mica" caps fool ya. Well, your milage may vary. I've clipped out at least a thousand old wax caps, two hundred plus plastic tubulars, and lesse, three discrete mica caps, and around eight of those wafer mica caps built into IF can bases. Mica's can go bad, they just don't seem to do so very often IMHE. |
SP-600 Rebuilding Experiences
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. |
SP-600 Rebuilding Experiences
"Ancient_Hacker" wrote in message ups.com... gkb wrote: Don't let the "mica" caps fool ya. Well, your milage may vary. I've clipped out at least a thousand old wax caps, two hundred plus plastic tubulars, and lesse, three discrete mica caps, and around eight of those wafer mica caps built into IF can bases. Mica's can go bad, they just don't seem to do so very often IMHE. Well, I've replaced 4 in my JX-17. That does seem unusual but I think they suffer from the same problem other molded type do, namely shrinkage of the case. These do not get leaky like the BB's but become very unstable. -- --- Richard Knoppow Los Angeles, CA, USA |
SP-600 Rebuilding Experiences
"Steve" wrote in message ... Richard, I performed an electrical restoration on an SP-600 (JX-26) last summer. The frequency accuracy was poor....WWV at 10 MHz was at 10.2 MHz (approx). What is worse IMO is the tracking across the bands. The frequency at one end would be high, but at the other extreme, it'd be low. I'm sure this can be tuned out. I just haven't tried yet. I'm in the process of bring back another JX-26 now, so if you have any specific questions, you can write me off list. Steve W6SSP Burried in the TM 11-851 handbook (p.35 I think) and in some Hammarlund advertising, I found a spec of 0.25% for dial accuracy. This isn't too bad for a conventional receiver. Also, I suspect the thing is capable of much better adjustment than this. My experiments will have to await getting over a back problem. -- --- Richard Knoppow Los Angeles, CA, USA |
SP-600 Rebuilding Experiences
"Chuck Harris" wrote in message ... Steve wrote: I'll second what Frank suggests about replacing ALL of the black beauty caps. I'm doing that now on the SP-600 I'm restoring. While none were a dead short, most showed some leakage, about 100K ohms. In many circuits, that won't cause a problem but in some its a big deal. About 1/3 had cracked cases. Steve Two things make the Sprague Black Beauty caps a problem, and both relate to their losing oil. The cap is molded out of a black plastic, with a small brass filler tube on the banded end. The capacitors were filled with mineral oil through this tube, and the lead was placed in the hole, and crimped. They then sealed the capacitor by adding a little bit of solder. So far, so good. Well, when the capacitors are installed, very often the banded lead is close to the lug that is being soldered, and it will carry the heat to the solder seal, and to the oil in the cap. The slight pressure increase in the cap will softly blow the solder out of the seal joint, and the oil will begin to seep out of the capacitor. Note: the oil is the dielectric, not the paper. Also, most all plastics will shrink over time, and the plastic the Black Beauties are made from is no exception. When it shrinks, the leads, and the filler tube do not, and you get a small crack, and a leak. If the oil is allowed to seep out, and the moisture is allowed to seep in, the capacitor will be compromised and become leaky. Also, without the oil, the WV of the capacitor is lowered, because the oil is the dielectric. Capacitors that are used near their WV will often arc over, and become shorted.... with catastrophic results for the rest of the circuit. -Chuck The BB's I found in the SP-600 are all of the dry Mylar type. I have seen BB's with oil all over them in other equipment. These were sold originally as highly stable, wide temperature range, replacements for the conventional paper type. Obviously something went wrong. The BB's I disected had glazed looking paper and attachment ferrules at the ends. They were not rolled up into a round tube but rather a quite flattened one. I don't know if this is how they were made or if its a result of the case shrinkage. In any case I agree with those who recommend replacing them at sight with disc ceramics. BTW, Sangamo also sold Mylar-paper caps in Epoxy dipped form. I wonder if these were any more reliable than the molded ones. -- --- Richard Knoppow Los Angeles, CA, USA |
SP-600 Rebuilding Experiences
"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 |
SP-600 Rebuilding Experiences
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 |
SP-600 Rebuilding Experiences
Steve wrote: Richard, I performed an electrical restoration on an SP-600 (JX-26) last summer. The frequency accuracy was poor....WWV at 10 MHz was at 10.2 MHz (approx). What is worse IMO is the tracking across the bands. The frequency at one end would be high, but at the other extreme, it'd be low. I'm sure this can be tuned out. I just haven't tried yet. I'm in the process of bring back another JX-26 now, so if you have any specific questions, you can write me off list. Steve W6SSP Thank you for the offer, I'm likely to take you up on it:-) At the moment I've put off a couple of projects because of a hurt back. Richard Knoppow Los Angeles, CA |
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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