High voltage checks - help please!

OutFishing2 · 1442

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Offline OutFishing2

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on: February 07, 2024, 11:06:43 AM
Hi, I have assembled my c2a and really enjoyed the build. I have hit a stumbling block on the voltage checks with a high result on KregA and various high voltages on all the boards. Please can I seek some help?

I will post voltage results and if it helps I can list the steps I've taken to chase down the error.

I should add I'm in UK so on 240v.

Thank you in advance!

David
« Last Edit: February 07, 2024, 11:16:51 AM by OutFishing2 »



Offline OutFishing2

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Reply #1 on: February 07, 2024, 11:13:46 AM
HP: T = 0.6mv steady whilst R cycles between 20mv and 50mv

LowVoltageBoard
IA = 197 (!)
OA = 66
KregA = 12.5 (!)
BregA = 172 (!)
IB = 172 (!)
OB = 72
KregB = 6.8
BregB = 196 (!)

High VoltageBoards
         RCA side    <>     PSU side
IA          198                    194
OA         196 (!)               170 (!)
bA          0                       0
IB            0                       0         
OB         108                   103
bB         196 (!)               170 (!)         



Offline Paul Birkeland

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Reply #2 on: February 07, 2024, 11:53:21 AM
Are +reg and Breg jumpered on the center board as shown in the manual on page 58 at the very bottom?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline OutFishing2

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Reply #3 on: February 07, 2024, 12:33:04 PM
Hi Paul,
Yes bridges look correctly done. Photo of my board attached for ease.
Thank you for the quick reply!
David
« Last Edit: February 07, 2024, 02:03:49 PM by OutFishing2 »



Offline Paul Birkeland

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Reply #4 on: February 07, 2024, 02:19:47 PM
What's the DC voltage on pin 1 of each 6AQ5 tube?  The Kreg voltages are plenty high to allow the regulator to work, but the absence of properly regulated voltages on both sides would point to some kind of repeated mistake on each side. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline OutFishing2

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Reply #5 on: February 07, 2024, 02:32:11 PM
I get 0v on pin1, consistent across both sides.



Offline Paul Birkeland

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Reply #6 on: February 07, 2024, 03:41:26 PM
Could you post a picture of the wiring around each 7 pin socket?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline OutFishing2

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Reply #7 on: February 07, 2024, 10:09:14 PM
How's this?



Offline Paul Birkeland

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Reply #8 on: February 08, 2024, 10:58:06 AM
It should not matter, but it might be worth double checking that you also see 0V at pin 7 on each 7 pin socket. 

I'd also be interested in the DC voltage present at the terminals marked X on the center C4S board, as well as a bottom shot of that center C4S board. 

I've also sometimes encountered oddball problems like this when the power supply feed going into IA is accidentally wired into OA, or the wire that's supposed to leave OA and feed the rest of the amp is instead fed from IA, though these issues are not necessarily indicated by the voltages you are reporting.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline OutFishing2

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Reply #9 on: February 08, 2024, 12:09:23 PM
Hi Paul,

So pin7 on the B & D sockets are each 0v.

X at the cap legs are 3.1v, descending slowly on A side and 3.7v ascending slowly on B.

I will double check all the OA / IA leads now.



Offline OutFishing2

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Reply #10 on: February 08, 2024, 12:24:51 PM
Power routing on the build looks as follows:

Terminal 24 to HighCurrent IA on RCA side
RCA side HighCurrent OA to terminal 6
Terminal 6 splits three ways to C2, LowCurrent IA and B5

B5 resistored to B6

LowCurrent OA to terminal 2
Terminal 2 splits two ways to A6 and C1

LowCurrent OB to A1 and C4 via terminal 4

LowCurrent IB to terminal 16
Terminal 16 splits three ways to C5, D5 and HighCurrentBoard PSU side OA
D5 resistored to D6

HighCurrentBoard PSU side IA to terminal 30






Offline OutFishing2

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Reply #11 on: February 08, 2024, 12:41:16 PM
Board underneath...



Offline OutFishing2

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Reply #12 on: February 08, 2024, 12:47:34 PM

Looking over the power routing reminded me of one anomoly I noticed in the build process. I don't think it's relevant but you may know better. On p61 there's an instruction to connect a short black wire between 1U and -reg and in the photo given, there's no sign of a longer black wire which was previously attached between 1U and high current board IB. I've built it with both wires in place.



Offline Paul Birkeland

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Reply #13 on: February 08, 2024, 12:56:56 PM
I would double check that the 431 regulators are in the correct spot, then resolder their connections if they are where they should be.  The 3V at X tells me that the 431 regulators aren't doing anything.   Also be extra certain that all those black jumpers on that center PC board are well soldered.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline OutFishing2

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Reply #14 on: February 08, 2024, 01:26:11 PM

I've resoldered the 431 regulators. They were in the right spots. No change to X volt readings and IA and KregA are still the same as posted yesterday.

Is it worth slotting in new 431s?

David