If you're looking for more headroom, Justa, then you're better off focusing more on the power tube than the preamp. Lowering the gain on the preamp tube mostly just drops the signal amplitude sent to power stage. The effect I've noticed is that it drops the apparent output volume, so that you'll need to turn the volume knob up further to get the same volume that you had with a 12AX7. But once you do, you'll get pretty much the same amount of breakup you got before, because the power tube is working just as hard, and it saturates before the preamp tube does.Originally Posted by Justaguyin_nc
What I'd recommend is to order a J&J EL84 from Bob Pletka at Eurotubes.com, specifying that it's for a Valve Junior and that you want max. headroom. He'll send you a power tube that has been specifically selected for minimal breakup. You might also want to get a 12AT7 while you're at it, so you can fool around with various tube combos and see what gives you the best result. As I recall, the J&J tubes use the European tube nomenclature, so you'd want the ECC81 preamp tube. Another preamp type you may want to check out is the ECC832. This is a 12DW7 type, a hybrid tube that's like half a 12AX7 and half a 12AU7 (which has a gain of only 20), with a gain factor very close to the 12AT7.