C2A build Voltage question

[TheRedMantra]

Hi friends. My C2A is SO close to being done. I did my voltage tests last night (resistance tests went perfectly) and got some weird numbers on the low C4S board:

IA 150V - 155V
OA 60-90V - 66V
KregA 3-6V - 1.9V
bRegA 150V -154V
IB 150V - 159V
OB 60-90V - 63V
KregB 3-6V - 1.9V
bRegB 150V - 164V

Before I start ripping everything apart is there a likely spot to start?

On the high current boards for the bA and IB measurements they're supposed to be 0V. I'm getting 0.1 for both on one board and 0.8 and 0.7 on the other. Is this acceptable? Do they need to be 0.0? I did have two LEDs not light up on one of the boards but noticed I installed them backwards somehow. I damaged one trying to remove it so I ordered replacements this morning and hope to have this all resolved next week.

Also, for the headphone jack, where do I measure "tip" and "ring"? I am not super knowledgeable when it comes to electronics and this is my first build. I can follow instructions and pay attention though 


Thank you for your help!

[TheRedMantra]

Might as well post values for the High Current boards if it can offer any insights or cause for concern:


Measurement - Board 1 / Board 2

IA 190v - 193/192
OA 150v - 169/155
bA 0v - 0.1/0.8
IB 0v - 0.1/0.7
OB 90-110v - 107/94
bB 150v - 169/155

These seem to be close enough but I am second and third guessing myself because I'm prone to confirming my biases. Haha!

[Paul Birkeland]

Can you post some build photos?

[Doc B.]

I'll throw out one possibility - are you measuring the Kreg voltages with a meter that does not autorange and, if so, are you using a high voltage range scale setting like 200V or 500V? Some meters with manually set ranges are not very accurate measuring smaller voltage values on the higher voltage ranges.

[TheRedMantra]

Doc, the meter auto ranges. Paul, I've attached a few pictures that will hopefully help.

I took these pictures AFTER the posted measurements. You can see I hammajammed the LEDs pretty good so that will be remedied when my new LEDs show up. Unfortunately my kit didn't come with any extras. And the powder coat is removed where the grounds need to make contact. That headache was solved with the forum luckily.

[Thermioniclife]

Looks like you should reflow all circuit boards usein more heat and solder to flow through the holes and onto the pads on the top side of the board.All the componants can take te heat except the led's and the small transistors.

[Paul Birkeland]

Looks like you should reflow all circuit boards usein more heat and solder to flow through the holes and onto the pads on the top side of the board.

Do this, but maybe don't do it for the LEDs on the PC boards, as they require very little heat to be soldered properly.

[TheRedMantra]

Thanks friends. I’ll try to get this sorted once the LEDs arrive. I learned to solder building this kit and it’s been a fun experience. I’m so eager to finally hear what it does!

[TheRedMantra]

The LEDs arrived and I replaced the two user errors. They lit right up. The faulty measurements didn't change so I started adding solder to all 3 boards. I backlight them to make sure no light was coming through the connections. Solid. I found two cracked white wires and fixed them up. KregB went to spec at 4.74V and KregA was still stuck at 1.91V.

I reworked practically everything. The KregA value was still the same. I thought why not swap the 6AQ5 tubes? The low value moved from KregA to KregB! KregA is now reading a healthy 4.74V and KregB is 1.91V. Does this mean I have a faulty tube?

For the jack I'm getting some weirdness too still. I don't know if this is because of a bad solder joint or it might be related to the Kreg issue? I'd love some insight on this as well.

Ring - 4V
Tip - 1.2-4.8V and it seems to go up and down and up and down while taking the measurement.
Sleeve - 0V

I want to plug my headphones in! I know the wait will be worth all of it. Thank you all for your help.

[Paul Birkeland]

Do not plug your headphones in until your voltages are correct. 

Are you sure you are seeing 4V at the headphone jack and not 4mV?

On the tube swap, it would still be worth checking that the 7 pin sockets don't have any pins touching  or loose connections, as the 6AQ5s are pretty robust.  Still, we can provide a replacement if that ends up being an issue.

[TheRedMantra]

I know, I'm being patient and won't plug them in until everything measures correclty. I double checked the headphone jack measurements and you are correct; they are in mV. Are those numbers low enough or is there an issue in the chain I need to find to bring them to 0?

I can redo all of the pin connections today on the 7 pin sockets and see if it helps. What puzzles me is why does the non-compliant Kreg value travel from the A side of the board to the B side when I swap the tubes? I visually checked and there are no pins touching.

[Paul Birkeland]

4mv is 0.004V, which is plenty low. 

The movement of the low Kreg voltage with the tube would suggest trying a new tube, but definitely keep an open mind that there may be something else going on that has to be tracked down later.

[TheRedMantra]

I appreciate that. I reworked all the joints on the 7 pin sockets and spent time cleaning up anything that didn’t look amazing. As my build progressed so did my soldering technique and going back to fix all the lesser connections was something I wanted to do anyway. Glad that’s done. I’ll call HQ at a more reasonable hr and see about a replacement tube. Thanks for your super quick responses Paul. A kit can be pieces and a manual. Bottlehead kits come with outstanding customer service and resources!

[TheRedMantra]

It turned out one of my 6AQ5 tubes was weak/bad. Bottlehead sent replacements and all the measurements passed. I’ve been using the amp for a little while now and it’s quite nice!