I recently (a month or two back) finished an ST-120 build with great success. At the time I was using them with 8ohm speakers, and adjusted the bias appropriately.
The other day my new speakers were delivered, but they're 4 ohm, so I cracked the case open again to switch to the 4 ohm takeoffs from the output transformers. It went without incident (I think...), but when I went to adjust the bias I found that the left channel was showing a ridiculously high voltage (30v) from the takeoff pin. The other 3 were, as expected, right around the .550v-ish mark.
Interestingly, there's nothing audibly wrong with the sound - When playing some test tracks everything sounds fine, as far as I can tell.
I don't know for certain that this was reading 30v before I switched to the 4ohm takeoffs, so it's possible it's unrelated, but it's the most recent change I've made, so I figure it's worth bringing up.
Any idea what could be wrong?