A year ago I bought a quad of Electro-Harmonix Gold Grid 300B's. I only fitted them recently and whilst enjoying them, one suddenly glowed brightly and the channel reduced in volume and became distorted. I switched off immediately and later checked out the amp but could find no faults to relevant components so concluded it was the valve that was faulty. I contacted Banzai and regardless of time passed since purchase, on return of the faulty valve they immediately sent me a replacement to match the rest of my original quad. Brilliant service and their prices are often lower than Hotrox and other suppliers in the Uk. banzai was originally recommended to me by James Doddington. Well worth a look.
http://www.banzaimusic.com