Re-tubing soon. Need advise: EL34, KT88, 6550

[hurdy_gurdyman]

Looking for opinions from a few different forums.

I've been
happily listening to my TAD-60 amp driving the Silver Iris OB speakers
for a couple of months now. The amp came with used EL34 (Svetlana) tubes.
Running them 8-16 hours a day, it's just a matter of time before
needing replacements. The amp is set up to take EL34, KT88 and 6550
tubes (triode and ultra-linear mode.) I'm looking for opinions on which
way I should go. This is a bit of a major purchase for me these days,
so I could use some experienced guidance here. Things to consider
include longetivity under long hours of playing, non-fatiguing high
end, taunt bass and good midrange for acoustic instuments. I'll be
listening mostly in triode mode (unless one of the other tube types
proves to sound better in ultra-linear mode.) I listen mostly to jazz
and folk with some classic rock thrown in quite a bit.

Here's the amp I use.

http://www.angelfire.com/biz/bizzyb/TAD-60.html

Here's the speaker drivers used (mounted on open baffles.)

http://www.hawthorneaudio.com/drivers.htm

Let's hear what you experienced tube rollers have discovered with amps that can do this type of conversion.
Thanks.

Dave

[NOSValves]

I would first contact Paul and ask him point blank what tube the amp was designed to run optimally. If I knew some basic spec's like what plate voltage it runs, the B+ current ability and the specs of the output transformer I could give you some pointers. Usually the case ends up with the best tube for a given circuit is the tube it was designed with while developing the product.

Craig

[hurdy_gurdyman]

Good idea. Why didn't I think of that?

Dave[:$]

[Daddy Dee]

In my stock MarkIII's which are stock UL, I have enjoyed Svetlana 6550's the most.