I should probably mention they are new, Russian-made Genalex tubes, not originals.
If you are on a budget and can't go to the Tung Sol KT-120 tubes I would say go for JJ KT88 Blue Glass tubes. In my experience with these tubes the sound and tone is clean but bass could be a bit thick. I've read that the JJ 6550 type tubes are just as clean sounding but the bass isn't as thick as the JJ KT88s.
One thing I find with the JJ KT88 tubes is that in my Jolida JD-502P it gets biased quickly upon turn on.
The Genelex reissues have had reliability issues, which may, or may not, be cured. I had one of my quad short out and there is plenty of other anecdotal reports about these on the Asylum.
The SED winged C seems to be the most reliable of the 6550/KT88 family in current issue, and the KT120, mentioned above by Brf has had great reports, though it pulls a bit of extra current and you should check with cj to make sure that it is appropriate for you amp.
Thanks for all the responses.
Elevick, "blow" may be a poor choice of words -- more like "fail" or "short." Definitely normal; the manual even reads:
"If an output tube shorts, this circuit will turn off the amplifiers main power supply by tripping the front panel circuit breaker, and light a red LED to indicate the defective tube(s). If this occurs, simply replace the indicated tube(s), reset the fault indication circuit (turning off any lit red leds), check the plate fuse, and rebias the amplifier."
Both amps were just serviced at c-j.
I have a pair of monos that use 4 tubes and tried a lot of KT88/6550 tubes (KR Audio, Genalex Gold Lion, EH, JJ, GE 6550 (1970) etc..) and once I heard the GEs, i had to sell everything else.
So clean and pure with lots of timbre and vibrancy.
If you have a Conrad Johnson amp, you should try the GEs. These are a must