Or are they night-terrors? I haven’t been able to get the tube amp in a mint tin idea out of my head. Assuming a suitable sub-mini tube type exists, the first obstacle is generating a B+ (48V or more) from battery power. For that, a DC boost circuit is in order. Of course, you should also have an easy way to recharge because whatever you build will probably eat batteries with complete abandon.
Here’s something untested and completely silly on the topic: