One last thing for now, I stumbled across a NOS channel knob on eBay.
After a bit of a struggle, I got the old knob off. The clear plastic fine tuning was filthy and got a good cleaning.
Here's how I've got the bulb sitting in it's holder. I'm not sure I've got it positioned quite right.
Here's what I got after fighting with it a while. I really need to setup a mirror so I can see what's going on while I position the bulb.
Even so, it's definitely better than before.