6550 tube vs KT88

For a comprehensive discussion and listening comparison of 11 variants of KT88/KT90/6550 tubes, see issue #19 of Vacuum Tube Valley. It can be ordered here.

Thanks Tvad I'll order that issue. I think the issue here is that my Seas speakers area MTM design rated at 87db, so its just not a match for the KT88 I demoed nor the EH88's that I rolloed in my JOR.
db rating must be 90+ to be effective.
This is the one drawback with Seas speakers, few tube amps can bring out the dynamics. The Jadis is one that can meet these demands, as their web site says, "our amps can drive any speaker" and they can. I've put their smallest amp to the test.
Not sure how the Jadis 88 tubes image? vs the 90's I'm using.
The thing is, if I order a Jadis amp in the future, I may just stay with the 90, as I like the sound. And may not be willing to give up the characteristics of the 90 in order to gain some benifits of the 88's or 6550's.
Trade off's are a part of this audio realm. But if it isn't broke, don't fix it.

Bartokfan,

>> I think the issue here is that my Seas speakers area
>> MTM design rated at 87db, so its just not a match for
>> the KT88
I do not understand this convoluted logic! what does 87dB SPL/W/m have to do with compatibility with KT88 output tubes?

what is the bias voltage set at for the KT88 tubes?
(for example, in my 502A the recommended bias voltage for 6550 tubes is 50mV. However, KT88 work better in this amp when their bias is set at 55mV i.e. driven slightly harder).

As far as I can tell: you do not have sufficient power amp output wattage to drive is mid-low efficiency speaker. Correct?
If so, please do not blame your lack of output power wattage on the sonics of the KT88!

Bartokfan, you should do some homework before writing, because you really don't know wtf you're talking about.

Your Jadis Orchestra (correct?) at 40wpc simply does not have enough power to drive 87db/1w/1m loudspeakers. It doesn't matter what tubes you're using. You don't have enough juice to recreate dynamic passages, especially in classical music. Period.

The following is taken from a review of the Orchestra here on Audiogon.

The limited power output means it struggles with vivid dynamic passages at loud volumes. It really can't render a concert grand without clipping - as a trial I'd suggest Emil Gilels' recording on DG of Beethoven's "Pathetique" - the chords crash and so does the amplifier. Yet, turn down the volume to what you might experience twenty rows back in an auditorium, and everything is fine - fantastic ambience, wonderful tone.

You might find some KT88 tubes that work well in the JOR, and they might be found in the Vacuum Tube Valley Issue 19, but your problem with the sound of KT88 tubes has nothing to do with the tubes, and everything to do with your mating of a 40wpc tube amp with 87db/1w/1m loudspeakers.

I owned a KT88 tube amp that produced 110wpc, and it created clean sound pressure levels of 105+db in my listening room with moderately sensitive loudspeakers like yours.

IMO, FWIW, Amen, All Praise to Allah.

Kumbaya.

Tvad, I beg to differ on a nit. Bartock fan does "know wtf" he's talking about. He understands himself perfectly. The problem is that nobody else does!

Perhaps in his ability to judge the performance of tubes sans amps (other than his JOR) and drivers without speaker systems (other than his Thors) his is an idiot savant, perhaps sans savant. For the life of me I don't know why anyone evens bothers to respond to his posts, they always evolove into a testimonial for KT90's (since I guess he decided against the KT88 based Cayin) and the superlative Seas drivers. I believe that is his initial intent when he posts. Too bad the word introspection is not one with which he is familar. If it were not so sad it would be funny.

IMHO, FWIW, Amen, All praise to Allah, and God Bless America............