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October 27, 2021, 09:01:28 AM

Author Topic: Help with voltage [resolved]  (Read 1702 times)

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Offline kill_surf_city

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Re: Help with voltage
« Reply #15 on: December 27, 2019, 11:19:45 AM »
A blue cap that gets hot could be in backwards, but I can't see that from your photos.

Caps are now put in properly.
Final readings before I do anything else

1.  84.6
2.  174.3
3. 0
4.  174.3
5.  116.8 *
6. 0
7.  107.6
8. 0
9. 130.3 *
10. 0

5 and 9 are out of range. Neither LED lights up.

Deke609

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Re: Help with voltage
« Reply #16 on: December 27, 2019, 11:35:38 AM »
I think you should wait for PB's input before powering the amp again.

But there is one thing I would suggest doing in the interim . See circled area in the attached pic: the black wire has too much exposed wire and looks like it might be touching (or might end up touching) the lead of the diode below it. If that happens, I think you'll have a short circuit every half cycle that will draw a ton more current than the transformer and diodes are meant to handle. I suggest reheating the joint and pulling the black wire further into the solder lug so that the bare wire and the diode lead no longer overlap.

I've also indicated with arrows what look to me like signs that the first 270 ohm resistor has been overheated - this is really just to bring it to PB's attention. I'm not sure if has been overheated, or even if it has, whether this is a problem. PB will let you know.

cheers, Derek

Offline kill_surf_city

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Re: Help with voltage
« Reply #17 on: December 27, 2019, 11:38:48 AM »
I think you should wait for PB's input before powering the amp again.

But there is one thing I would suggest doing in the interim . See circled area in the attached pic: the black wire has too much exposed wire and looks like it might be touching (or might end up touching) the lead of the diode below it. If that happens, I think you'll have a short circuit every half cycle that will draw a ton more current than the transformer and diodes are meant to handle. I suggest reheating the joint and pulling the black wire further into the solder lug so that the bare wire and the diode lead no longer overlap.

I've also indicated with arrows what look to me like signs that the first 270 ohm resistor has been overheated - this is really just to bring it to PB's attention. I'm not sure if has been overheated, or even if it has, whether this is a problem. PB will let you know.

cheers, Derek

Got it. Thanks!

Edit: there was actually a pretty good amount of space between the wire and the diode but I pulled the black shielding further over anyway.
« Last Edit: December 27, 2019, 11:45:31 AM by kill_surf_city »

Online Paul Birkeland

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Re: Help with voltage
« Reply #18 on: December 27, 2019, 05:56:13 PM »
Do both halves of the 12AU7 still glow?  Your voltages tell me that one half is not conducting.

Do not listen to an amp that hasn't passed its voltage checks.  Those tell you whether or not the amp is working properly, and an amp that isn't working properly can destroy headphones.  (In fact having the 100uF cap in backwards will melt one headphone driver if you tried to listen to the amp like that, if you put a bulged cap back in and attempted to listen to the amp, you may have already caused some damage)
Paul "PB" Birkeland

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Offline kill_surf_city

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Re: Help with voltage
« Reply #19 on: December 28, 2019, 03:36:10 AM »
Do both halves of the 12AU7 still glow?  Your voltages tell me that one half is not conducting.

Do not listen to an amp that hasn't passed its voltage checks.  Those tell you whether or not the amp is working properly, and an amp that isn't working properly can destroy headphones.  (In fact having the 100uF cap in backwards will melt one headphone driver if you tried to listen to the amp like that, if you put a bulged cap back in and attempted to listen to the amp, you may have already caused some damage)

Yep. Both sides of the 12AU7 glow.

Offline kill_surf_city

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Re: Help with voltage
« Reply #20 on: December 28, 2019, 08:31:00 AM »
Do both halves of the 12AU7 still glow?  Your voltages tell me that one half is not conducting.

Do not listen to an amp that hasn't passed its voltage checks.  Those tell you whether or not the amp is working properly, and an amp that isn't working properly can destroy headphones.  (In fact having the 100uF cap in backwards will melt one headphone driver if you tried to listen to the amp like that, if you put a bulged cap back in and attempted to listen to the amp, you may have already caused some damage)

Do you think the cap needs replacing? That’s what I’m thinking since I seem to be having the voltage problem with the left side (Terminals 5 and 9). Also I only listened to it after I had put the bulged cap in properly. I’ve listened to my headphones since with my other amp and there doesn’t appear to be any damage.

Online oguinn

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Re: Help with voltage
« Reply #21 on: December 28, 2019, 08:32:20 AM »
You could post more pictures of the cap and the rest of the build. If you don’t have a way to test its capacitance you could just buy a new one since they’re not super expensive.
Jameson O’Guinn

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Offline kill_surf_city

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Re: Help with voltage
« Reply #22 on: December 28, 2019, 08:40:11 AM »
You could post more pictures of the cap and the rest of the build. If you don’t have a way to test its capacitance you could just buy a new one since they’re not super expensive.

Here’s some pics

Online oguinn

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Re: Help with voltage
« Reply #23 on: December 28, 2019, 08:45:45 AM »
I’m not an expert at this at all, so maybe PB disagrees, but I’d replace that cap before I ran electricity through the amp again.
Jameson O’Guinn

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Offline kill_surf_city

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Re: Help with voltage
« Reply #24 on: December 28, 2019, 08:52:55 AM »
I’m not an expert at this at all, so maybe PB disagrees, but I’d replace that cap before I ran electricity through the amp again.

That’s what I was thinking. Ordered a couple new ones last night from Mouser. Thanks!

Online Paul Birkeland

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Re: Help with voltage
« Reply #25 on: December 28, 2019, 11:23:05 AM »
Yes, that cap is damaged.
Paul "PB" Birkeland

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Re: Help with voltage
« Reply #26 on: December 28, 2019, 06:12:50 PM »
You can run the amp with no 100uF cap to continue debugging the issue you're having up front with those DC voltages that aren't correct.  Do both the LEDs on the 9 pin socket illuminate still?  At least one must be lit, but perhaps not both?
Paul "PB" Birkeland

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Offline kill_surf_city

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Re: Help with voltage
« Reply #27 on: December 30, 2019, 10:15:29 AM »
You can run the amp with no 100uF cap to continue debugging the issue you're having up front with those DC voltages that aren't correct.  Do both the LEDs on the 9 pin socket illuminate still?  At least one must be lit, but perhaps not both?

I have both the caps in right now. I’m gonna remove the bad one. But as of right now, neither LED comes on. I think one comes on initially then fades out.  But I’ll have to let you know for sure.

Offline kill_surf_city

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Re: Help with voltage
« Reply #28 on: December 30, 2019, 10:50:11 AM »
You can run the amp with no 100uF cap to continue debugging the issue you're having up front with those DC voltages that aren't correct.  Do both the LEDs on the 9 pin socket illuminate still?  At least one must be lit, but perhaps not both?

Okay, so as it stands with the cap damaged cap still in, the LED connected to A8 initially turns on when I plug it in then fades out. The other LED stays off. What should I look for?

Online Paul Birkeland

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Re: Help with voltage
« Reply #29 on: December 30, 2019, 10:58:02 AM »
The LED should not turn on when you power up the amp.

Does this also happen with no tubes in the amp at all?

Can you post a fresh photo of just the 9 pin socket wiring?
Paul "PB" Birkeland

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