6550 to KT88

Be very very careful with the JJ KT88s. Their reliability was a disaster for me with them not lasting more than 6 or so months. Upon destruction, they launched a power resistor in the amp (ARC VT130) each time. I went back to 6550s, lost a little of the midrange warmth but gained a more neutral tonal balance and reliability to boot.
John

Thanks for the warning . I was considering the JJ's.

Jaq , Your concern over JJ is realistic but a maddening tradeoff because they do have the best tonal qualities of any current KT88.Both JJs I bought from a well known Canadian tube dealer went bad frying 2 different ASL amps--- expensive repairs both times.The word from a previous thread about this stated that KT88s are the most easily damaged tubes and do poorly in shipping. Try finding a vintage amp that uses 7591 power tubes. This is great tube sound.

Hi,
I rolled the svetlana 6550 and ei's kt90 on a pair of jadis Ja-30 before i changed to the Jadis se300b's.
I loved the 6550 over the kt90 although the lost of punch on the bass region. The mids and highs never sounded more sweet and relaxed. Since I´m using 93db on the low octaves the less power on bass wasn´t an issue. The great "BUT 2 here is that mids are made with a vintage jbl driver and horn and are very sensitive to "Harshness". I think in a regular dome midrange-high driver the kt90 maybe the best way to go.

I have no major differences of opinions of the various tubes types, but as JaFox noted the JJ was (still is?) very unreliable. In fact of the new production tubes the only ones I have not experienced major failures with yet are the Svet 6550's (my primary tube of choice when combined in my amps with EI 6DJ8's). In fact one of my mono's is in the shop right now - I tried out a new set of KT88's - boom! - tube, resistor, and fuse went south. So did $150. I've got to learn how to solder.