Tube replacement questions from a beginner...

My epiphone galaxie 10 has clips rather than soldered leads for the speaker. Your epiphone might be similar. And indeed, I would have to take out the amp chasis to get at the speaker, it is half hidden behind.

One thing you could do is to add a cab and some sort of jack so that you can cut out the internal speaker when you plug into that jack. I've been thinking about doing this to my Galaxie 10 -- basically, build a small 1x12 cab and use it as an external speaker. But, I've been following the "why break it when it's not .." policy :-)