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.