09-07-2016, 09:01 AM
(09-07-2016, 08:38 AM)neddyboy Wrote: Hi Liquids, thanks for the reply. Flyback diodes would be a first for me. Would those be D7-D10? All the amps I've worked on have been simple 2-tube PP Fender-ish designs -- this V4B is pretty intimidating! FYI definitely not plugged into the ext.speaker jack, and I swapped a set of KT66s in to rule out the KT88s as the problem. That's a drag to hear about the EH KT88s. Did the blown tube take out any amp components?
Yeah, D7-D10 are the flybacks. You can simply disconnect them carefully and audition if there is a difference.
I wouldn't mess with KT66s! I don't think most (any?) can spec out to handle the V-series plate voltages--and that's just for starters there!
While you are in there, make sure your screen grid resistors are at least 1K since you are using KT88s and such--that's not a bad move here even if using 6L6GC types.
When the KT88 went, it only took out the fuse given the resultant current draw. When I replaced the fuse I switched it on very cautiously with an eye on the power tubes, and switched it back off immediately as I saw the intense glow from that KT88--quick enough to save even that new fuse from blowing.
Everything else was fine, and I've overhauled the amp, so I would have been miffed if virtually anything was taken down because of that tube. I only used the KT88s in there as I had gotten them for another project I was going to do and never did. I've had the most luck with quality 6L6GC type tubes...even cheap, but rugged unbranded Chinese 6L6GCs have held up better then most of the other non-6L6GC tubes I've messed with on a limited basis.