I'll be converting a stock Dynaco PAT-4 solid state preamp into the ULTIMATE mod for the PAS-4 - an SP12 tube preamp.
I've done several of these using my PAS3 mods, but wanted to do something nicer and better with this chassis. Cost was $60.
Add an SP12 board, throw in a couple of leftover power transformers from other projects, about $300 worth of parts total,
and a budget SP12 in a vintage style chassis . . .
OR, you could do the exact same thing but using an SP9 board if you want tone controls, the PCB is the same size and price.