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  #16  
Old 08-13-2017, 08:29 PM
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jr_tech jr_tech is offline
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Was thinking that these old high meg resistors might behave in a non linear fashion when current is passed through them. Voltage drop comparison during operation under load might reveal some odd behavior.

Pin 3 & 6 measurements with the 7N7 pulled might reveal socket problems if the voltage is still low with the tube pulled.

grasping at straws,
jr
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  #17  
Old 08-13-2017, 08:53 PM
Crist Rigott Crist Rigott is offline
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Quote:
Originally Posted by jr_tech View Post
Looking reasonable... have you tried another 7N7?
Does the voltage drop across r-99 match r-102 and r-100 match r-103?
C-5 ok?

jr
I just saw this. Let me get back to you.
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  #18  
Old 08-13-2017, 11:24 PM
Crist Rigott Crist Rigott is offline
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Quote:
Originally Posted by jr_tech View Post
Looking reasonable... have you tried another 7N7?
Does the voltage drop across r-99 match r-102 and r-100 match r-103?
C-5 ok?

jr
Yes, I swapped out V13 and V12 both 7F7 with no joy.

C5 is good. I removed the C5 wire from pin 7 of V13 and gator clipped in a new 10uf 450V cap. No joy. Restored the wire.

Measured the voltage at the junction of R99 and R102 = 400V, the junction of R100 and R103 = 500V. R100 ohmed out to 2M while the others at close to 2.2M.

Voltages at V13 with the tube pulled are pin 3=1120V, pin 6=1020V.

Tried subbing C81 and C80 at the same time, no joy.

Both pin 3 and pin 6 of V13 drop down when the tube starts to conduct.

I ohmed out the vertical transformer and it ohmed out pretty close to specs.

I'm at a loss right now.

I appreciate your help and suggestions.
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  #19  
Old 08-14-2017, 12:32 PM
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jr_tech jr_tech is offline
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For grins.... what voltage do you measure on v-13 pin 7?
Do you have another 7F7? unlikely both are bad, but possible.
Do you have a scope? I could measure a few waveforms for comparison. I need to bring the Philco back to the bench to replace the seleniums, that I forgot about, anyway.

a real headscratcher,
jr
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  #20  
Old 08-14-2017, 10:07 PM
Crist Rigott Crist Rigott is offline
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I found the problem. I thought that it really wasn't a height problem but more of a severe fold over at the top of the picture. I looked in my TV trouble shooting book and it listed severe fold over and to check the coupling capacitors. Bingo! It was 100pf 500V mica C78. It is connected between C82 (the HV cap that I replaced last time I had this problem) and pin 4 of V13 the 7F7 vert. amp.

Now I have a lot of cleaning up from a lot of troubleshooting!

Thanks for all the help everybody.
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  #21  
Old 08-14-2017, 10:28 PM
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jr
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