Bottlehead Kits > Crack-a-two-a

Voltage issue with High Current C4S

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Toobuzz:
Hello,

I built the Crackatwoa and listened for a day. It was outstanding and great fun to build, of course. I also changed out the caps and listened some more. Today I installed the Twoquiet along with some bigger caps. Once I completed the Twoquiet upgrade I ran the resistance checks and all passed (still do). I then registered the following voltages:

Low current C4S
IA 107
OA 73
KregA 1.1
bRegA 107

IB 148
OB 70
KregB 3.25
bRegB 148

High Current C4S (B tube socket)
IA 195
OA 107
bA 0
IB 0
OB 78
bB 107

The other higher current board measures perfectly. After going through the manual twice, I focused on the bad high current board. I removed the jumpers and all excess solder/flux. I took my time and reflowed all pads and ran new jumpers. I also inspected, checked for continuity/resistance all connections on the B tube socket as well as solder lugs 6-10.

Here are the new voltages:

Low current
IA 49
OA 33
KregA .36
bRegA 49

IB 148
OB 70
KregB 5.5
bRegB 148

High current
IA 198
OA 49
bA 0
IB 0
OB 30
bB 49

The B side LEDs of this HC board also went out after reflowing and reattaching the board. All 4 LEDs on the low current board have not illuminated since attempting this upgrade.

Was I correct to focus on this HC board?  Is there something that these numbers suggest I focus on next? 

I may do the same rework on the low current board but I’m just guessing at this point. She was working great before doing the Twoquiet and that upgrade didn’t really touch any of the areas that seem to be giving me issues. Any help would be greatly appreciated!



Sam

Toobuzz:
I reflowed the A side of the low current board and ensured all connections were clean around terminals 1-5 and 11-15.  I even reattached the white wire on pin 2 of the 7-pin socket under the offending board. I swapped the 7-pin tubes and am still getting these second set of voltages from my OP. Is there some way to rule out a bad transistor?  I suppose I could swap the high current boards, and if the issue doesn’t follow the board then I must be missing a mis-wire or short.

Paul Birkeland:
Can you tell me about the soldering products you're using?  I would very strongly recommend not adding flux to your build, as there is already flux in your solder.  If you pull both 6AQ5 tubes and run the amp, does the offending voltage pop back up? (It should go up closer to 200V)

Toobuzz:
I use a Hakko FX-888D and Cardas Quad Eutectic.  I’ve never used flux on any of my builds, although I sometimes wish this solder was a smaller gauge. After pulling the 6AQ5 tubes I only see a small difference in voltages.

LC
IA 60
OA 40
KregA 0
bRegA 60
IB 205
OB 70
KregB 1.25
bRegB 205

Would swapping the high current boards help isolate the issue?

Paul Birkeland:
Which flux does your Cardas solder have?

Are you 100% certain this build was working prior to the modifications? 

Next I would pull the wire out of the IA pad on the low current board that goes to 6U, then see if the voltage at OA on the high current board pops back up.

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