Voltage checks on the large board higher than expected post speedball install

[Robert]

I just finished the assembly & installation of the Speedball. I ran the crack stock for about a month before starting the upgrade.

Small board installation went fine, and voltage checks passed within bounds. Large board installation resulted in voltages outside of the expected ranges (lb - OA +24%, lb - OB +16%) . Visual inspection and some cursory re soldering of suspected joints resulted in no change. Some simple tracing of connections resulted in consistent voltages back to the tube. So, could use any ideas. Mains voltage is ~120V.

Voltage checks post large board install (5 mins after plugging in to allow for stabilization):
Large board:

• OA  123.8V
• OB  116.3V
• G  0.9mV
• B+ 183.2V

Small board:

• OA  86.4V
• IA  183.0V
• B0A/B  0.7mV
• IB 183.1V
• OB 94.2V

Voltage checks post small board install: (tested and listened to after install per manual)
Small board:

• OA  86.6V
• IA  171.9V
• B-A/B  0.9mV
• IB 171.7
• OB 93.4V

And, for the sake of completeness, here are the voltage checks from when I finished the stock crack, before any of the speedball upgrades:

• T01  88.7V
• T02  172.6V
• T03  0.9mV
• T04  172.6V
• T05  96.1V
• T06  0.7mV
• T07  111.3V
• T08  0.9mV
• T09  118.1V
• T10  0.7mV

Pre and post install pictures attached.

[Paul Birkeland]

Those are close enough that I wouldn't worry about it.  You have a combination of a 12AU7 that's at about 75% of optimal and a 6080 that's quite potent, and that will land you in a spot like this.

[Robert]

Paul, thanks for the quick reply (and the sanity check)!

Gave it a listen, and it sounds great after it has had a few moments for the circuit to power up and the voltages to stabilize.

I did hear some pops and crackling when I first turned it on, but that went away after a few powercycles, and I have not heard it since. I am guessing that is somewhat normal (or can be)?

[Paul Birkeland]

Noise during turn-on isn't super uncommon with old thermionic valves.

[kurogle]

Hi Paul, I didn't want to create a new post since I have similar readings... My OA and OB on the large and small speedball board are a bit higher than Robert's. Do you think this is still in ok range?

Large board:
OA 130V
OB 131V
G 0V
B+ 185V

Small board:
OA 106V
1A 185V
B-A/B 0V
1B 185V
OB 100V

1-5 same as above
6 0V
7 130V
8 0V
9 126V
10 0V

Also, I re-soldered the entire board and had the same readings before and after.
Re-soldered because I heard a loud buzz in one ear and my original solder points were poorly done. Upgraded to a Hakko iron and WOW now I know my previous iron wasn't getting warm enough.
Previously, all the little HLMP-6000 LEDs would turn on at different intervals over ~10+ seconds. Now they all nicely turn on all at once in a few seconds! Hope that's a good sign.

Thank you,
Kurt

[Paul Birkeland]

The soldering beneath the Speedball raises some questions.  What kind of solder are you using, and what kind of iron?  I see some joints that aren't well heated (A4, A5, and A6).

[kurogle]

Hi Paul,

I'm using "60/40 Solder Tin Lead Rosin Core Solder Wire For Electrical Soldering" with Hakko FX-888DX.

Pics attached of the A4 A5 A6 joints.

[Paul Birkeland]

That looks better.  The 100V outputs on the small board could be a 12AU7 that's not super duper fresh, so you may not have an actual issue.

[kurogle]

Oh wow you're right I swapped the stock 12au7 for a newer one I have and the OAs and OBs dropped:
Larger board:
OA 109V
OB 108V
Smaller board:
OA 70V
OB 72V

Is it bad to use a tube that causes higher voltage? I have a few other tubes, do I need to test them....does it affect the tube or the crack negatively? Or just don't worry about it anymore and enjoy my crack....

Thanks for the quick responses Paul, you're awesome!

[Paul Birkeland]

That's OK to use, but the amp should sound a little better with the fresher tube.