C4S LED and voltage issue

Loquah · 2850

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Offline Loquah

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Reply #30 on: May 12, 2020, 09:12:54 PM
Quote from: Paul Birkeland on May 12, 2020, 07:01:53 PM
OK, so the OB voltage that really wanted to spend the rest of its life at 6V has popped back up without the regulator in the way.

I believe your issue will be resolved by replacing the 431 regulator on the offending channel, with the slightest possibility that you'll also need a 12AU7. 

-PB

Thanks Paul - I appreciate your help and patience. I've ordered the required parts and will advise once installed
« Last Edit: May 12, 2020, 11:30:14 PM by Loquah »

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Offline Loquah

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Reply #31 on: May 14, 2020, 10:23:39 PM
I've replaced the TL431 and swapped in a fresh 12AU7. All voltages are correct EXCEPT Kreg (B side) is still reading only 6V.

All tubes are new compared to when original issue arose.

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Offline Paul Birkeland

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Reply #32 on: May 15, 2020, 05:22:27 AM
Are you able to adjust the bias per the instructions in the manual?

Paul "PB" Birkeland

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Offline Loquah

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Reply #33 on: May 15, 2020, 03:22:41 PM
Yes! I think the A-side trim pot was out of range if there's such a thing. A few extra turns and I'm back in range.

Thanks so much, Paul. Can I ask one more question?

Should I be wary of trying any of the previous tubes back in the amp? If the tubes have failed could they cause problems if I reinsert them?

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Offline diynewbie

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Reply #34 on: May 16, 2020, 01:15:57 AM
Good question, looking forward to Paul's reply.  I would suggest that you download data sheets and use your meter to check for shorts.


Offline Paul Birkeland

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Reply #35 on: May 16, 2020, 04:43:38 AM
The amp should tolerated shorted 6C45PI tubes pretty well.  Things will heat up if you leave them in there running for a long time though.

Paul "PB" Birkeland

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Offline Loquah

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Reply #36 on: May 16, 2020, 03:25:11 PM
Quote from: Paul Birkeland on May 16, 2020, 04:43:38 AM
The amp should tolerated shorted 6C45PI tubes pretty well.  Things will heat up if you leave them in there running for a long time though.

Thanks, Paul. I'll fire it up quickly, check for sound (with sacrificial test headphones) and respond accordingly

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