#16
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Pin 4 of horiz output tube is way off. It SB 150v then goes thru a 6.8K, then a 4.7K to a 330v source. I have 295V at pin 4 all the way thru the resistors and at the source.
I replaced the 6.8K resistor. The 4.7K checks about 5.3K and I have to get one of those. The 1st paper cap I replaced was the .05 coming off pin 4 to ground. I have also replaced the .05 coming off pin 2 of the flyback. |
#17
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A fellow member is mailing me a Sams for the set, so I can't do too much until I get it. I did notice that I have no negative grid voltage on the 6BQ6. I should have -8V. I have about -.5
The 82ohm resistor on the grid measures about 95 ohms, so I'm sure it's good, |
#18
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Right after my last post, I found part of my voltage problem. Instead of a 6BQ6, there was a 6DQ6 in place. Putting the right tube in gave me the propr negative voltage.
The screen grid voltage is still way off. I should have 150, and I have about 55 volts. The 330V source is only reading about 220V. I'm going to star tracing where the source voltage comes from and see what's wrong. |
#19
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Some Success:
I decided to try another damper tube. The one in there was the original CBS. I now have a horizontal line across the screen. Most all the paper caps have been replaced except a couple in the audio section. I'll start tracing the vertical section tomorrow. |
#20
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I think I've located my vertical trouble. The primary in the output transformer is open. Does anyone have a Stancor A-8141, Merit A 3039, or Chicago TSO-12 for sale?
Thanks Doug |
Audiokarma |
#21
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My vertical output transformer came in, but I don't have full vertical deflection. Picture goes about 3/4 to the top and bottom. I've found that my B+ is down 90 volts. I should have 340V, and I have about 250. I've been unhooking things trying to find the problem, but it is still a mystery . Later on today, I will post part of the schematic to see if anyone can shed light on this .
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#22
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Ok here is where I'm at. I've been waiting on a new damper tube which arrived today, and that did not correct my voltage problem. Something is pulling the 340B+ down to about 240V.
I finally discovered when I disconnect pin 8 on the flyback, the voltage returns to normal, however the 330V then drops to about 125v. I feel the flyback is working since I have HV. I've posted some closeups of the SAMS to show where the 340V is distributed. |
#23
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Can you post the part of the schematic showing the power supply? Need to see if the center tap of the 5U4 winding goes thru some resistor(s) or directly to ground.
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#24
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Sure thing. Here is the power supply. The 60 ohm resistor R106 is one of those sand coated ones that have not replaced but is checking good. If you think that could be the problem, I'll order a new 60 ohm resistor.
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#25
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If the 60 ohm resistor checks good it's not the problem. Is it running unduly hot by any chance? Have you subbed the 5U4 with a known good one? What's the B+ voltage directly at the 5U4 filament?
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Audiokarma |
#26
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Voltage directly off the filament of 5U4 is 268V. Have tried another 5U4. R106 SB 60 ohms and it measures 66 which is close enough. I did order another one, since the one in there is the old sand coated unit. I had planned on replacing it anyway. BTW the voltage at that resistor on the center tap is -12V.
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#27
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Ok, I'm stumped. It seems the flyback on connection 8 is what is pulling down the 340 volts. I feel like the flyback is good because I have plenty og high voltage.
In the power supply circuit, C3 SB a 25uf at 12 V. I had a 160V in there, and it shorted out. Today, I bought two 35 volt units. I put one in, and it exploded after about 40 seconds. Right now I have a 450V unit in there. Here is the raster on my screen currently. The power supply and Hv section of my Sams are a couple of posts back, if someone could look and see possibly what may be wrong. Thanks |
#28
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Have you checked 47 ohm resistor R100? If it's open, it would blow up C3.
What's the AC voltage at the plates of the 5U4 (measured from ground)? OOPs! Scratch that. I forgot the 5U4 is mounted on top of the power xfmr. And you probably don't have a Pomona adapter. Last edited by old_coot88; 05-05-2016 at 10:44 PM. |
#29
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You do not have the polarity of the replacements backwards, right?
__________________
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 |
#30
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Here's what I found out. With pin 8 f the flyblack disconnected, it puts full B+ across that Cap C3 which caused it to explode. Connecting pin 8 back up pulls the B+ down to 250V BUT only puts about 3V across that cap. The original cap was a 12V unit.
R100 has been replaced When I started on this set, I 1st replaced C1A and C1B. I have since re replaced them but that hasn't helped. Could it be in the flyback even though I have good HV? |
Audiokarma |
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