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  #46  
Old 04-16-2015, 01:16 PM
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wa2ise wa2ise is offline
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Quote:
Originally Posted by Electronic M View Post
Stacked B+ ain't a bad thing and worked well
You're making use of energy (some going to the audio speaker) that would have been wasted as heat in a power resistor. And the audio tube acts a little like a voltage regulator, after some filtering to remove audio.
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  #47  
Old 04-17-2015, 11:17 AM
sylvania sylvania is offline
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I was reading post from Electronic M. Checking my audio output tube 6W6GT is shows immediate short on my tester but under load on tester it is showing in good range, this could be some of the problem with set. I had checked these tubes twice before.Guess it went shorted under load.
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  #48  
Old 04-17-2015, 12:55 PM
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The set could be damaging the 6W6, or it could have just been a problem tube that got worse from use. I'd look for voltages out of speck on that tube. One thing to beware of is autobias on the tube (don't know if it is used in your set or stacked B+ sets, but suspect it is). If it is off the tube could be conducting too hard and get worn out prematurely, or conduct too little and have other issues.

Autobias basically uses a lowish value cathode resistor to 'ground' (in your set its a lower B+ rail) and connects the grid to the 'ground' through a high value resistor. The resistor is chosen so that if a specific current flows through it it will create a voltage difference between cathode and the grid that makes that current flow....Basically it's a feedback loop with all static values dependent on the cathode resistor value (assuming no defects elsewhere).

One thing comes to mind assuming a modulated channel with no sound or significant noise if the 'sound control' is volume and drives the grid of the output, but is isolated from that grid with a cap the cap may have failed and the control may be skewing the no sound bias of that grid outside of the designed range.
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  #49  
Old 04-20-2015, 12:08 PM
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I checked voltages and I suspect that is causing wear on tube. Sams shows pin#3 is supposed to be 150v my reading is 287v. Pin #4 Sams shows 140 my reading is 274v

Last edited by sylvania; 04-20-2015 at 02:22 PM.
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  #50  
Old 04-22-2015, 01:36 PM
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Audio Output tube Voltage

Audio output tube voltage is wrong, Pin 8 shows 125v which checks correct. But on pin 3 I have 287v Sams shows 150 and pin 4 I have 274v Sams shows 140.What would cause this? I have checked resistors and wiring and can find nothing wrong or out of spec any ideas? And this is set at 108v if I raise it to 117v I am getting over 300v on these pins. On pins 3 and 4 shows large dot Sams say this is measured from 125v line
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Last edited by sylvania; 04-22-2015 at 01:37 PM. Reason: more information
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  #51  
Old 04-22-2015, 01:54 PM
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what are 5 and 8 voltage? the screen and plate are prob high due to a dead tube or incorrect bias (5 and 8).
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  #52  
Old 04-22-2015, 02:09 PM
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What is the voltage on the 125V line? There are a few possibilities that come to mind....Such as the audio out transformer could have a shorted primary, or the tube could be conducting much less than it should be (which could be caused by a few things).
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  #53  
Old 04-22-2015, 02:29 PM
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sylvania

I checked pin 5 voltage is 105v pin 8 122v my 125 volt line is 132v.I checked this tube 6W6GT it shows good no shorts. the old one had a short. I have a very dim picture and sound is ok some interference using my DVD player I can tune most of it out with fine tuning.

Last edited by sylvania; 04-22-2015 at 02:38 PM.
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  #54  
Old 04-24-2015, 11:08 PM
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Audio Output tube voltage

I will try to make this clear as I can, The audio tube 6W6GT pins voltages are wrong. I have over 300v on pins 3 & 4 Sams shows It should be 150 & 140v. Pin 8 Sams shows 3v I read 125v. Pin 3 Sams shows -11 I have + voltage on that pin. My audio was not sounding clear until I lost high voltage while troubleshooting voltages then it cleared up, so the high voltage was causing interference with sound. Upon checking why the high voltage quit I found the two damper tubes 6V3A and one horz output tube 6BQ6GT went bad. I check voltages on all other tubes and they were to spec and checked resistors have not found but a few out of tolerance. I had a dim picture and sound until high voltage quit, but as time went by picture got worse. Now have sound only. Until I get voltages correct on tubes what is the best way to protect the high voltage section? I see a lot of different theory's on how to protect the high voltage section.
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  #55  
Old 04-25-2015, 08:09 AM
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is there anything in the sams legend about the large dot next to the voltage readings?
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  #56  
Old 04-25-2015, 08:25 AM
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voltage readings

Sams says large dot reading taken from 125v line, I have 125 volts on that line.
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  #57  
Old 04-25-2015, 08:42 AM
DaveWM DaveWM is offline
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so when you read those you are reading from the pin and the 125v line NOT the pin and the ground, correct?
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  #58  
Old 04-25-2015, 09:12 AM
sylvania sylvania is offline
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Yes that is correct, I assumed that was what I was supposed to do.
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  #59  
Old 04-25-2015, 10:52 AM
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Well i found part of problem, a resistor was going open when warmed up. Now try to figure out what happen to HV section.
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  #60  
Old 04-25-2015, 12:07 PM
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Quote:
Originally Posted by sylvania View Post
I will try to make this clear as I can, The audio tube 6W6GT pins voltages are wrong. I have over 300v on pins 3 & 4 Sams shows It should be 150 & 140v. Pin 8 Sams shows 3v I read 125v. Pin 3 Sams shows -11 I have + voltage on that pin. My audio was not sounding clear until I lost high voltage while troubleshooting voltages then it cleared up, so the high voltage was causing interference with sound. Upon checking why the high voltage quit I found the two damper tubes 6V3A and one horz output tube 6BQ6GT went bad. I check voltages on all other tubes and they were to spec and checked resistors have not found but a few out of tolerance. I had a dim picture and sound until high voltage quit, but as time went by picture got worse. Now have sound only. Until I get voltages correct on tubes what is the best way to protect the high voltage section? I see a lot of different theory's on how to protect the high voltage section.
so when you connect the postive of your meter to pin 8 and the neg to the 125v line you get 125V so you are getting a voltage drop 125v across that 68 ohm resistor?
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