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Old 18th March 2008, 03:07 PM   #11
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I might have damaged the mosfet again initially while reconnecting the ground. The output tube grid voltage is positive again and fluctuates. Iíll give it another try later today with my remaining spare mosfet. Thanks.
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Old 19th March 2008, 12:55 AM   #12
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Default Update

Replaced mosfet and solved the problem with R14. Now for 5842 plate to ground voltage check, both sides are adjusted to 175 vdc but right side (earlier problem) tube is glowing brighter in about a minute after the power up. I switched the tubes but the right side still glows brighter. Could it be something to do with R10 and 16?
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Old 19th March 2008, 01:32 AM   #13
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It is possible that the U2 chip could be damaged in a way that allows too much current to pass. I have only seen this happen, but it was in my amp and it happened after I was poking around in a live amplifier with a scope probe. Measure the voltage across R16. It should be about 3 volts to give 10mA. If it is significantly higher, the chip is toast.
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Old 19th March 2008, 02:29 AM   #14
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Default Just as I feared.

Yup, the voltage across R16 is 8.4 vdc. That was my last spare chip so it's time to order again. It may be the longest few days coming up for me.

Thanks for the help.
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Old 25th March 2008, 01:49 AM   #15
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Default More updates

I replaced the damaged U2 chip. Once the rectifier tube warmed up, I saw a spark at the base of leads where the chip is soldered to the board. What could be doing this now?
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Old 25th March 2008, 02:58 AM   #16
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Quote:
I replaced the damaged U2 chip. Once the rectifier tube warmed up, I saw a spark at the base of leads where the chip is soldered to the board. What could be doing this now?
If you saw a spark there is either something causing a short on the board, like a small solder fleck, or there is a cracked trace on the board, and you saw an arc jumping the gap.

I am at a loss to figure this out without seeing the board. Please send me an email.
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Old 25th March 2008, 03:11 AM   #17
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I MIGHT have pulled a pad off my tubelab pcb. It was for an unused pin on one of the tubes, so no big deal. I was also doing some not so standard soldering of little copper tubes to the pads. On the other hand, I might have not heated the pad up enough, so it was just a cold solder joint that came loose. I say MIGHT, because the solder came up perfectly flat as if the pad released from the pcb, but the pad on the PCB was still gray, tho not shiny. I didn't do any further testing because the pad isn't used.

Anyway... I've pulled pads off of plenty of small home made PCB's in the past from overheating, and that was with a lower temp iron.

Point being.... check the continuity from the legs of those chips to whatever it is they connect to next on the PCB.
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Old 25th March 2008, 03:11 AM   #18
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Email sent.
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Old 25th March 2008, 04:49 AM   #19
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Default My fault once again

Looks like bad solder was it. Another rookie mistake.
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Old 25th March 2008, 05:30 AM   #20
wicked1 is offline wicked1  United States
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Well... good.

What makes someone an expert is that they've already made almost every possible mistake.

(im not in any way implying im an expert. i have many many more mistakes to make. When it comes to tubes an amps, I'm still working on my first one.)
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