Crack + Speedball Voltage Question [resolved]

[Hudson]

Hi,

I noticed that the voltage on OB on the Speedball board sits at around 115V. It lists a range between 75-100VDC. Is this OK even though 115VDC is technically outside of the 10% variation of 100VDC? OA sits at about 105VDC.

I should note that it appears to be functioning fine (I saw another forum post where 115V was ok, but only if both OA and OB were the same, which is not exactly the case with mine). Is this discrepancy just due to the 12AU7? Or should I cease use of the Crack with the upgrade installed?

[Paul Birkeland]

There are a few things that can happen to make this the case.  If you have a 12AU7 with moderate emission, that may result in plate voltages on the 12AU7 being around 85V or so on each side.  If you pair that with a very high emission 6080, then the bias voltage required to hit 30mA of operating current can be a bit on the high side, and you'll end up with more like 110V on the outputs of the big C4S board rather than the typical 100V.

[Godaisan]

i Hello,
I just installed the Speedball upgrade and I am getting an OA voltage of 111V and an OB voltage of 176V.  Any ideas where I could have gone wrong?  Thank you in advance for your assistance.
Cheers

[Godaisan]

Also the OA is reading 178V on my small board now too.  Thanks again.

[Godaisan]

I think I fixed it now.  The voltages are now + or - 10%.  They are 110 and 106.  Looks like the 12au7 wasn't fully seated.  Thanks all.