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#76
03-09-2013, 11:34 AM
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Hi All;
I have a room full of smoke.. Two resistors burned up.. Need to find out IF I have something wired wrong, either to the Electrolytic or the internals of the cap.. Or the External wires to the Cap or drawing too much current or wrong size (wattage) of the resistors.. The Cap is C223, the two resistors are R140 (3300) and R141 (6800).. Which is right in the area of where I have my Suspect bad socket and trouble.. 1ST Video Amp.. (6AU6) THANK YOU Marty Last edited by Geist; 03-09-2013 at 11:41 AM. 
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#77
03-09-2013, 01:03 PM
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Quote:
It's very unlikely C223(b) is involved. If it had shorted, only R141 would have fried, leaving R140 unaffected. That tells you the short has to be 'downstream' of R140. With the tube pulled, and with R140 disconnected, put your ohmeter (on highest ohms scale) on pin 5. It should show infinite resistance (open circuit) to ground. Any measurable leakage would be a fault condition. Last edited by old_coot88; 03-09-2013 at 02:22 PM. Reason: Corrected "pin 3" to read pin 5.
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#78
03-09-2013, 02:20 PM
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WOOPs! Error (sound of klaxon)..
The 6AU6 plate connection "Pin 3" in the foregoing post should be pin 5 Sorry for the goof. 
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#79
03-09-2013, 03:13 PM
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Hi All;
I used 99% alcohol, but I think it might have been the other stuff I tried to used that might have done the trick (possible short).. Old Coot, No problem for the mistakes, I make plenty of my own.. Yes, I will ohm it, as well as check all the other surrounding components.. Thank You, Old Coot for the circuit analysis, I sure wish I had your ability.. Anything else that sticks out that I should look at ?? THANK YOU Marty
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#80
03-09-2013, 03:38 PM
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Hi All;
I measured Pin 5 to ground its OK.. But, the look of pins 7, 4, 2, and 1 don't look so good, I can't at this point tell IF it is from what I did, or just old gunk on the bottom of the sockets after spraying the tube and socket.. THANK YOU Marty
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#81
03-09-2013, 04:43 PM
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Quote:
Even though pin 5 showed no leakage to ground on the ohmeter, i would try "zapping" it briefly with full B+ to see if an arc develops. Use a current limiting resistor (value not critical, 4.7K or thereabouts) and jumper it briefly from pin 5 to the filament (pin 8) of the 5U4. If an arc should develop in the 6AU6 socket, it'll be instantly visible.
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#82
03-09-2013, 07:27 PM
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Gads, talk about me overlooking the obvious. Have you checked the 6AU6 for shorts? The schematic shows the suppressor grid (G3) connected directly to ground. A G3-to-plate short would certainly fry those two resistors.
G3 and the plate are physically adjacent inside the tube, making them quite vulnerable to shorting.
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#83
03-09-2013, 08:10 PM
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Hi All;
Old Coot, I'LL check both the tube and the various connections of the Tube.. The Tube was a NOS (1971).. But, I guess it could be shorted, either internal or external.. I am done for the Day, But, I will hopefully check it monday.. If there is no work.. I have a whole list of things to check.. Thank You.. THANK YOU Marty
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#84
03-11-2013, 12:53 PM
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Hi All;
While I am at it, should I spark, with 300+ volts, pins 6, 5 and 1.. I have disconnected the parts from these pins.. Pins 2, 3 and 7 are ground, and pin 4 is the other filament connection.. So these last four connections would not get sparked.. Pin 4 shows a resistance reading of .1 on the Sams, and I have .6 on it to ground (pin7).. THANK YOU Marty Last edited by Geist; 03-11-2013 at 01:29 PM.
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#85
03-11-2013, 02:55 PM
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Hi All;
I Just got a Junk chassis only 8TS30 for parts and to compare connections in all the Electrolytics and also in the Video section, which is attached to an electrolytic.. The only difference that I see between the two is that the 8TS30 used a Choke and its bigger.. And the 630TS uses a Field Coil.. Tube placement looks the same as well as what and where the Electrolytic caps are located.. THANK YOU Marty
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#86
03-11-2013, 03:20 PM
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I've been following along with your progress and I don't recall any mention of replacing the paper caps. Are you running it on the originals ?
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#87
03-11-2013, 03:47 PM
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Hi All;
Bandersen, Yes, as that is the next big expense, I knew it might have some that were bad, but, I have always brought it up with the Variac.. And so far they seem to be ok.. I know that the problem with Video section might be the caps.. I just Re-looked at the schematic and If either is shorted there could be a path to ground.. And of course cap leakage.. THANK YOU Marty
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#88
03-11-2013, 04:29 PM
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I was goin' on the assumption you had replaced the caps. For the present issue with the video, at bare minimum you should change the grid coupling caps C138, C140, C141 and C142. They're all .05 (or .047).
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#89
03-11-2013, 04:55 PM
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Hi All;
No, I had always said electrolytics, couldn't aford to do both at the same time.. That is the next thing to do, I need to make a list of what I need and find them.. Not sure if Mouser or Digikey or Allied.. Will need to compare prices.. Does anyone have any suggestions as to who has the bast quality and prices ?? THANK YOU Marty
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#90
03-11-2013, 07:01 PM
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I measured all of my 630TS paper caps for value and leakage current. Out of 35 paper caps I only found 4 with no leakage current and also within 50% of their marked value. Only one had no leakage and close to its marked value. So yeah, you REALLY want to replace all the paper caps!
Dave
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