Have a Blue Beetle 15 watt combo amp with a DI but no external speaker options. Looking at getting a Bell and Howell extension speaker. Is it possible to modify the DI to a 1/4 jack or would one just add a 1/4 jack to the amp?
You can use a DI out for connecting an extra power amp. This is generally not the best option – in particular, a DI-out is usually before the master volume control, i.e. you won't be able to use that for independently controlling the stage volume anymore. Also, you obviously won't have that output available for its intended purpose (connecting to the mixer).
But for guitar tube amps, miking the cabinet generally gives a better sound anyway and volume can't be controlled independently of sound, so in this case I'd say using the DI for an extra speaker makes just sense.
Alternatives you could try are:
- Using the FX send (that's basically just a line-out, but spliced out even earlier in the signal chain)
- Splitting the signal before the amp entirely and feeding an independent other amp in parallel.
- Using a DI in the speaker line (make sure to connect the parallel to the combo's speaker!). This is the only option that gives you the full sound through the power tubes and volume control, which is usually a good thing. Possibly the Blue Beetle's DI-out is actually wired this way already, I don't know.
It's up to your test, and taste, which option you like best.
I'd also remark that I doubt you need your amp louder at all. Electric guitarists are usually too loud on stage; the main exception I've encountered is, curiously enough, particularly guitarists with overpowered amps who are forced to turn the master volume way down, which leads to both difficult to control levels and suboptimal sound – basically you lose the characteristics that make it worthwhile to have a tube power stage in the first place.
Therefore I consider low-power amps which emphasize on quality over quantity (that seems to be the idea behind the Blue Beetle as well) an extremely good idea. Likely the issue is not that your amp is too quiet but that you yourself don't hear it well enough. That should be adressed by placing the amp closer to your ear, or by abolishing the amp-as-monitor concept entirely and relying on the wedges or in-ear monitoring instead. If you go this route, you'll allow your band to have a much clearer overall sound. (Of course you may not want that, but I'd say it's always better to err for clarity – adding dirt into the sound is easy, removing it is hard.) Some bands even place the amps off stage entirely, in soundproofed cabins which also allow the cabinets to be miked easier.