A3 LED not lighting and terminals 5/9 are not giving proper voltages [resolved]

benf925 · 1299

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Offline benf925

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on: May 28, 2019, 06:44:22 PM
I recently finished assembling by stock crack. The resistance levels were all correct when I tested them. When I turned on my amp with the tubes in place, I noticed that only the A8 LED lit up. I went to test the voltages listed in the manual and all were acceptable except for terminals 5 and 9.

I am getting 153V at terminal 5 when it is supposed to be 50-100.

I am getting 151V at terminal 9 when it is supposed to be 90-115.

Both tubes seem to light up correctly. I tested the voltages at both LEDs with the power off. The A8 LED appears to be posting a very small number of volts in both directions while the A3 LED is showing 0V in both directions.

What can I do to fix this entire situation?

Thanks
-Ben
« Last Edit: May 28, 2019, 07:37:27 PM by Paul Birkeland »


Offline Paul Birkeland

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Reply #1 on: May 28, 2019, 06:45:51 PM
The LED going to A3 doesn't look soldered at A3.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline benf925

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Reply #2 on: May 28, 2019, 06:53:04 PM
The A3 pin/LED is soldered together. I apologize if the picture was not clear.


Offline Paul Birkeland

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Reply #3 on: May 28, 2019, 06:54:45 PM
4U and A4 are also slightly suspect.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline benf925

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Reply #4 on: May 28, 2019, 06:57:00 PM
Do you mean that they look to be not/poorly soldered?


Offline Paul Birkeland

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Reply #5 on: May 28, 2019, 07:01:33 PM
It looks like there may be some solder on the back of 4U.

Do both halves of the 12AU7 show glowing dots?  A4 looks like maybe it needs a little more heat, but if you have both halves of the 12AU7 glowing, I wouldn't worry about that.

What are the DC voltages at A2 and A3?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline benf925

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Reply #6 on: May 28, 2019, 07:08:20 PM
Both sides of the 12AU7 tube are lit looking at the bottom. A2 is getting 0V. A3 is getting 13.90V.


Offline Paul Birkeland

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Reply #7 on: May 28, 2019, 07:13:46 PM
The LED going to A3 is open.  This can happen if the kit has sat for a very, very long time in a humid environment (think 6+ months in a garage in Hawaii), or from lots of overheating.  The good news is that you can connect A3 and A8 together and that will resolve your issue.  It is up to you if you want to replace the damaged LED, but there's no harm in running with A3 and A8 connected together.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline benf925

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Reply #8 on: May 28, 2019, 07:16:47 PM
So I should keep everything the way it is and simply add and solder a piece of wire going from A3 to A8? Will this also fix the issues I am having with terminals 5 and 9?


Offline Paul Birkeland

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Reply #9 on: May 28, 2019, 07:22:31 PM
Yes.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline benf925

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Reply #10 on: May 28, 2019, 07:35:25 PM
The voltages are correct now. Thank you so much!


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