Gee, I'm RIGHT aGAIN!! I said, keep it simple. Tubes are the weakest component in a tube amp. Seen it, done it, been there. On live events, tube amps crap out, guess what, ya don't say oh well, let's get it to a shop, try the tubes FIRST, it's 99.99% the tubes! Now what else? Reality based troubleshooting, what a concept! Been doing it for 30+ years, experince beats nonsense all the time. Anyone who uses tube electronics and don't have spares of all teh tubes in teh thing is foolish, they crap out, and many times all of a sudden Can I hear an AMEN, JV, you owe me this one!