I got this power amp and I would like to convert it for guitar use. I plan to dump the 6J5 tubes and use the sockets for a preamp and PI instead. I haven't been able to find any useable schematics for a 4x 6V6 PPP design. I have some 6SN7 and 6SJ7s I can use. Any thoughts on what I can do with what I have here?