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Old 8th September 2011, 01:12 AM   #21
Jpeg is offline Jpeg  United States
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Hmmm, I may owe you $10 then... I got very similar results to yours, which is what lead me to suspect this. It does sound like that is not the issue though...Sorry.
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Old 8th September 2011, 01:37 AM   #22
Jpeg is offline Jpeg  United States
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Since you have yours is not in a case, just for fun, Try clipping your test leads to tab on your tube socket that supples pin one, and pin 9. These are the two pins on either side of the gap. (where there is no hole in the socket) get a DC reading, then turn the pot for that tube as far as it will go in the other direction and get another reading. Mine reads about about 50 volts on one side of the pot and about 175 on the other, what do you get?
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Old 8th September 2011, 01:46 AM   #23
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Shoot, looks like you logged off while I was testing mine. This will rule out a bad spot on the pot, or too high resistance shutting it off all together, that kind of thing... I might be completely off base...again, but it should only take a minute to try.
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Old 8th September 2011, 01:57 AM   #24
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Quote:
Originally Posted by Bola View Post
Ok, here it is:

Without tube (still heat from heatsinks):

Ground to:
R16 tube: 17V, R16 IC: 449V, both sides: 0V
R17 tube: 17V, R17 IC: 17V, both sides: 0V
R27 tube: 17V, R27 IC: 449V, both sides: 0V
R28 tube: 17V, R28 IC: 17V, both sides: 0V
R10 & 32 both sides: 0V
OK, that is very telling. There should be no current through R16/27 with no tube in there. You should measure close to B+ on both sides. The fact that you see 17V on the plate side tells me that you either have a short in your socket wiring, your coupling cap (C9/11) is shorted, R16/27 are blown, or there is some weird PCB problem. In fact, you measurements imply that R16/27 are dissipating 1.3W. Do they get toasty?

I would expect to see 0V across R10/32 at this point.

Quote:

With tubes on (heat from heatsinks):

Ground to:
R16 tube: 6V, R16 IC: 13V, both sides: 6.5V
R17 tube: 6V, R17 IC: 6V, both sides: 0V
R27 tube: 3V, R27 IC: 10V, both sides: 5V
R28 tube: 3V, R28 IC: 3V, both sides: 0V
R10 & 32 both sides: 0V
Ground to tube: 6.6 & 4.25V

I tried for potential poor coupling cap (I rised one leg for both coupling cap) = no change in the data.:

I checked again for potential shorts - nada.

I also grounded the board to the grid - nada.

However, both tube sockets are hooked up through 4 inches of wire (not directly welded to the board). Am I facing oscillations or some weird phenomena?

My next step is to change both ICs. I don`t have a good feeling for the end result but I need to give it a try...

Alain
It could be oscillations, but that doesn't explain your results with no tube installed. Why is the plate voltage 17V with no tube in there? It makes no sense.
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Old 8th September 2011, 03:06 PM   #25
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Quote:
Originally Posted by Jpeg View Post
Shoot, looks like you logged off while I was testing mine. This will rule out a bad spot on the pot, or too high resistance shutting it off all together, that kind of thing... I might be completely off base...again, but it should only take a minute to try.
Sorry Jpeg, I did not realize you were online trying stuff for me. No mean to waste your time. I have a small window of time every night to work on the board (between homework with kids, lunches, cleaning the house, walking the dog - you get the picture)

I going to try tonight what you proposed.

Thanks again.

Alain
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Old 8th September 2011, 03:10 PM   #26
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Russ,

I was under the impression the smell was coming from the IC but you are probably right, the smell is from the resistors.

OK, tonight I will remove completly the sockets. The coupling cap are already removed. When I clean up my mind from those potential sources of problems, very little would be left and I hope to put my finger on it tonight.

More to follow

Alain
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Old 9th September 2011, 01:21 AM   #27
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I think I got it! R16 and R27 installed are 330K!!! Instead of 330 Ohm.

I don`t have 330 with me but I have 250 and 100 (total of 350 Ohm). I will try that for tonight and I need to weld back both sockets.

Alain
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Old 9th September 2011, 01:28 AM   #28
rknize is offline rknize  United States
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That makes sense. Easy mistake to make when ordering too. I've done it before.
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Old 9th September 2011, 01:40 AM   #29
Jpeg is offline Jpeg  United States
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Fantasic, glad you found it!
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Old 9th September 2011, 02:04 AM   #30
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I changed resistors, re-connected sockets, powered up everything, and.............. Yessss!

I was able to adjust to 175V both channel!!!

Oups, my wife is telling me it is time to stop for tonight. Tomorrow, I will plug speakers and a source. I just cannot wait!

Many thanks to you guys, Russ and Jpeg for all that support. Without you I would still be crying in a fetal position on the floor!

Alain

Last edited by Bola; 9th September 2011 at 02:27 AM. Reason: typo
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