Tube amp debugging question

I recently pulled my old Trace Elliot SpeedTwin C50 amp out of storage. It's a 50W, all-valve combo amp. 5 12AX7s in the pre-amp, and 2 EL-34 power tubes. The amp has a clean and a distorted channel.

I power it on, and the clean channel works great and sounds beautiful. However, the distortion channel doesn't work at all. No noise or anything, just silence, no matter how I fiddle with the knobs.

What's the probability that this is caused by something simple (i.e., one of the 12AX7s is blown) vs. something that I'll have to find someone who works on valve amps to fix?