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In Reply to: KT90 is mind blowing! Good heavens this tube rocks! posted by DevoX on November 07, 2002 at 17:53:14:
Does anyone know how long these tubes last. I have them in an amp made probably 1992-1993 and have been wondering if they are about to run out anytime soon.
What signs should I be looking out for to suggest that these tubes are due for replacement?
Thanks.
Follow Ups:
I have just got my first set, so I can't really comment with authority. However, I did read that the KT90 is a real work horse and is tough as nails. It apparently lasts a very, very long time and can take quite a bit of abuse.-- Robert
Hi there,my two cents on the topic:
First, I have to admit that in the PP amps I tried them I was not
entirely pleased with the sound - preference went to EL34 or KT88
- in Ultralinear-Pentode operation - however, in a SE triode-wired
setup the pair I listened to was quite outstanding, beating the living
daylights out of the GE 6550s they replaced.As for the lifetime, the ones in the SE amp - using the permissible
anode dissipation in full, lasted for less than 1000 h before getting
dull - by loss of emission. This happened twice in a row, with matched
pairs from a reputable importer.A shop owner I know uses them as standard in the Jadis gear he sells.
The pre-tested ones from Jadis last 2000-4000h, whilst his trial of
stuff directly imported from the factory did deliver mixed results,
with life between 200h (and subsequent runaway with deformation of
the anode and other electrodes) to 4000 h. Some were gassy and
therefore useless out of the box.It seems that there is (or has been) an issue with the QA of EI.
As for the good examples, they are _very_ sturdy. The intestines are
based on a horizontal line deflection valve for TV sets, the EL519,
which gives the valve catodes with high impulse current resilience...Best regards,
---mb---
======
Try again: EL156 .This was the tube that DM brought to the Ei factory's attention. He wanted an AUDIO tube, a super KT88/6550-type, higher plate dissipation, tolerant of high voltages, octal based, no plate cap, and definitely NOT a horizontal deflection TV tube.
If he wanted TV tubes we could have gotten EL519's cheap all day long and saved oruselves all the hassle.
While it is true that Ei were making EL519, and the innards might appear to look similar, it is very important to make the distinction that the KT90 design was NOT based on this tube.
As for tube life, that will depend on the amplifier design, and plain ol' good luck. I have documented cases of KT90's running +50,000 hours in recording studios in LA, in our amps, never switched off, in a dedicated air-conditioned rack.
Cheers, EveAnna Manley, Manley Labs
Please correct me if I'm wrong. But wasn't the KT90 (or KT99 which I believe are basically selected KT90)based on, or "inspired" by the old Luxman 8045G that was manufactured for them by NEC? They look very similar except that the KT90/99is a little taller. The internal elements look the same too, except for being proportionately larger to fit the taller glass envelope. I also believe Gold Aero was rebranding KT99 & converting them to 8045G by rewiring & new base. I have some of these & they are nearly a direct replacement in the Luxman MB3045 amps (for which the 8045G was designed) requiring only the repositioning of an existing resistor on one of the socket pins.
I beg to differ.The tooling used by EI for anode as well as for the mica discs is the one used for their 1980ies EL519s - the grid configuration is different, but the anode looks like a carbon copy.
I challenge you to do the comparison.
The EL156 is somewhat different - it is based on the LS50-family,
and a real pentode. These two and the EL152 share the basic configuration, but differ in the envelope, connection layout and internal capacitances, as the latter was optimised for VHF use.
The EL153 is similar, too, but a tetrode with beam former...This is easy to see - just take one of each and look at it.
Mr. Manley may have intended to get a EL156, alas, this did not deliver. The KT90 is a reasonably good beam power valve, but it is nowhere near the EL156 in properties.
Compare the curves.
If you are in for a _good_ EL156-clone, they are produced in China now.
If you are in for an interesting beam power valve, take the KT90.
Regards,
---mb---
======
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