🚀 go-pugleaf

Finally, after many years of use, the tubes in my amplifiers rather
spectacularly bit the dust.  I am now realize that I'm in a more
precarious position than I expected.

First I sent off for one matched pair of KT88's.  Of course, these
are of Chinese manufacture (apparently no one else makes 88's these
days).  They lasted about 3 hours.  Initially they had a rather high
grid current (gassy tube), but one eventually flashed over.  The next
day most of the getter had turned white - a very gassy tube.

I ordered another pair from another supplier (in California).  To make
a short story shorter, they lasted longer than the first, but eventually
died the same spectacular death.

For years I've listened to others complain about the state of modern
vacuum tubes, but now their points really hit home.

I am left in a position that I don't really have a easy solution to.
I am considering the following:

1)  Substitution of New-Old Stock 6550's.  They bias slightly differently,
and I don't have a clue where I could buy a matched pair.
2)  KT90's?  They're supposed to be a more refined tube than the 88's.
I may have to do some circuit tweaking (don't know yet).
3)  KT99's?  This is quite a different tube than the 88's or 90's.  Made
by Tesla in the Czech Republic, it definitely will require some circuit
modifications.  Sonic Frontiers uses them in their amps, and apparently
they like them a great deal.  I don't know anyone other than Sonic Frontiers
who supply them - and they want an arm and a leg for a matched pair.
4)  EL34's?  This would require a more radical circuit modification,
but in principle this would be possible.  EL34's apparently never went
through the same decline as KT88's, since they're in such widespread use
among musicians (ie., Marshall amps).  This has been a much bigger market
than the audiophile market, and will very likely continue to be so.  This
option has the best *long* term prospects (from what I can see).
4)  Go back and get another pair of Sino KT88's.  I really don't want
to do this.

Does anyone out there have any comments or suggestions?  Any help
would be greatly appreciated.

Adam  <duff@phenom.physics.wisc.edu>