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#16
10-26-2014, 11:11 AM
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6KD6 horizontal output 6MJ8 (not lighting) 6BV11 (gassed out) 12HG7 6LU8 6LX8 6CG3 6KV6A regulator 3DF3 rectifier 6AQ5A (hiding behind power supply filter cans) New chassis pics. I had to switch off full auto to make the camera flash and not blur the pictures, but I got rid of the custom white balance settings used for a pic I took long ago. https://www.flickr.com/photos/spacec...57638419636316 https://www.flickr.com/photos/spacec...57638419636316 https://www.flickr.com/photos/spacec...57638419636316 Last edited by Jon A.; 07-10-2015 at 06:31 PM. Reason: Didn't notice the 6AQ5 until now. 
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#17
10-26-2014, 01:13 PM
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This shows at least 2 Sams 1281 I have & another I dont.
Compliment I have 6KD6 hoz out 6LU8 vert osc / out 12HG7 video out 6MJ8 r-y, b-y, g-y amps 6BV11 demodulator 6CG3 damper 3DF3 HV rect in cage 6KV6 HV regulator behind cage 6JW8 horz osc. May be a production change or a sub. It is near the coil. 73 Zeno 
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#18
10-26-2014, 02:29 PM
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It appears that the 6JW8 and the 6LX8 differ *only* in heater current requirements:
http://www.radiomuseum.org/tubes/tube_6lx8.html Should make no difference in a set with 6.3 volts supplied to the tubes from a power transformer. Nice job of fixing the pictures! jr
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#19
10-26-2014, 04:03 PM
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Am I right in guessing that bad HV rectifier/regulator tubes will not cause CRT damage like bad safety caps in SS sets? That reminds me, I saw white caps under the chassis but I have no idea if they're safety caps.
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#20
10-26-2014, 05:55 PM
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When the cap failed, it allowed the HV to soar to 50 KV or higher, which exceeded the dialectric strength of the glass. Bleed-through resulted in thermal stress in the glass which sheared off the neck slick as a whistle. Tube sets could only make 30 - 35 KV when the regulator failed, which wasn't enuff to hurt the glass. In reading the tube complement of your set, I was hoping to see a HV regulator tube listed. Are you sure there isn't one lurking back there somewhere? If not, the set uses the nefarious feedback regulation setup which was very problematic. Hoping yours is an exception to the rule. Last edited by old_coot88; 10-26-2014 at 11:49 PM.
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#21
10-26-2014, 06:09 PM
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a tube job. Only thing that may is arcing at the anode that etches into the glass & cant to my knowledge be fixed. Seen that once. Maybe a burning yoke could do it to. White caps are always suspect & AFTER you know you got a good CRT may be best to change them. IMHO at this point the best thing is to get the HV up & see how good the CRT is with minimal investment. Quick lesson The hoz osc drives the horz out. The hoz out runs "class C" so is turned off most the time. If the horz osc is running OK there should be a large negative voltage on the hoz out G-1 ( -75 VDC) on pins 5 & 9. If the negative voltage is not there the tube is on all the time & it will soon glow red & even melt but the breaker sees the heavy current & pops. Thats the short story but things after the H out can load it down & cause the same thing. Often when you get it going the H out is weak or bad, usually width is in but you can judge the CRT at that point. 6KD6's are used in home brew HAM amps so they bring a premium price. Maybe if you need one a kindly soul on the list can help, it was a very common tube.......... 73 Zeno
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#22
10-26-2014, 06:41 PM
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By the way, I have an extra 25V pulled from a real basketcase that hopefully will work without too much trouble should the original prove weak. Last edited by Jon A.; 10-26-2014 at 06:45 PM.
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#23
10-26-2014, 07:51 PM
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I do not think so...the final "dense hybrid' color sets--with under 10 tubes--often did not use any regulator tube at all. Our beloved 4 tube Zeniths are a good example. Nothing much more than a VDR or 2 to control the voltage applied to a feedback ckt from the flyback--tied in the grid ckt. of the H-out tube. I suspect this is quite similar. By 71--NO set used a shunt reg. I think--and not nearly all used a pulse reg (such as the 6KV6 or 6HS5). By that time--mfg's were finding it easier to eliminate them--just using a vdr or 2 as the reg.element.
STILL my favorite--is the old reliable 6BK4 shunt reg. tube--as used in my 1969 or so Sylvania D-12 set--I think it has 9 or 10 tubes or so. FULL SS audio and IF. One is a shunt reg, one is an HV rect. Later sets that used triplers eliminated both of those tubes--such as the D-16 set.
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#24
10-26-2014, 08:26 PM
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d 12?very,very good sets.those and the d 16 chassis sets were awesome.love to have a few of those now
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#25
11-01-2014, 01:15 PM
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By the way, is it safe to power up with missing tubes? The 6BV11 is toast of course, and I'm hoping that I can check for those negative voltages with the hoz out removed. I updated my tube complement list in post 16. Last edited by Jon A.; 11-01-2014 at 03:28 PM.
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#26
04-11-2015, 12:42 AM
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Well, I finally got to test the CRT. Low emission on all three guns, the red gun being especially bad. Also, it's had a lot more use than I first thought; I discovered a lot more black dust, so instant play is not totally to blame for the CRT's condition. I know just about all delta-gun CRTs are electrically the same, but which ones will sub directly for a 25VABP22?
I finally noticed a switch next to where the power cord goes in. No indication as to what it does, it's simply marked "on/off". It can only be accessed by removing the rear panel. I'm hoping it disables instant play. I discovered a cracked resistor, R545 near the horizontal output tube.
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#27
04-11-2015, 12:14 PM
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My sam's sub manual lists:25VADP22, 25VAJP22, 25VALP22, 25VAMP22, 25VBMP22, 25VCGP22, 25VCKP22, 25VDAP22, 25VDEP22, 25VDXP22 as subs.
This manual likes to cross 3 letter tubes to 3 and 4 letter tubes, but to only cross 4 letters to 4 letters. If you have a spare 3 letter type I can try to cross it forward to a 4 letter type and see if that crosses back to a 25VABP22.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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#29
04-11-2015, 04:25 PM
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BTW are you aware of the phenomenon of CRTs being asleep? In a nutshell if a good tube is not used for a few years gas inside the tube gathers on the cathode and forms a coating which blocks emission. The coating can be boiled off if you run the tube heaters at 1.4X their rated voltage for about 10 minutes give or take. Any weak tube that I don't know the full history of gets the 'cooking' treatment before I write it off...And most bounce back well.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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#30
04-11-2015, 10:24 PM
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I have heard of it but didn't know anything about it. I did hit all guns with auto-restore more than once but it didn't bring satisfactory results.
Another thing that I had never seen before in a tube that was still under vacuum: the phosphor coating looked, for the lack of a better word, uneven around the middle of the screen. I cleaned it, no difference. Last edited by Jon A.; 04-11-2015 at 10:33 PM.
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