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Old 30th March 2006, 04:05 PM   #11
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Quote:
Originally posted by SY
plate/screen really shouldn't be run over its (probable) 150-200V rating.
More injury to an opened wound...Implying..What tube have we got here with such low ratings ? With such a phantom sized anode, one of the biggest in it's class implying with it's mediocre performance it's hardly worth assembling the blighter in the first place. Coke B'le 807's would perform better and per se more reliably.
My vendor wouldn't risk playing foul with me, I did mention on my previous lot < no foul up's on these and check'm simmering at 500V> (that was 88's).... however there are vendors who would just sell a tube for a cheap buck and say it works and one gets a short lived ticket.. (We get fed up returning phony tubes in the post..)

I'm going out to shovel some snow......blue glowing anode (sky) overhead.
I know there are EH KT90 types around. The question becomes one OF which batch...? 7/10 bad... rest av..

It seems I might have to pay up/ settle for JJ 88's and be content.

richj
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Old 30th March 2006, 09:40 PM   #12
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Mine were personally brought back from Bosnia by a former resident. They were also tested at the factory and hand picked before they left the factory.
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Old 31st March 2006, 08:50 AM   #13
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Quote <<ask Jim McShane for KT90>> I certainly did and replied <<avoid'em>>. Many thanks SY (you were right) and others who commentated.

KT90 for me is for claypigeon target

richj
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Old 31st March 2006, 11:44 AM   #14
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Quote <<ask Jim McShane for KT90>> I certainly did and replied <<avoid'em>>. Many thanks SY (you were right) and others who commentated.

KT90 for me is for claypigeon target

richj


I will set up a test jig and check some of my KT90's. Give me the voltages and I'll let her rip.
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Old 31st March 2006, 01:47 PM   #15
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Put 150 volts on screen and plate. Do a sweep of gid voltage from, say, -50V on down, monitoring plate current to see if you've got a high perveance tube on your hands.

I understand rich's frustrations 100%, but it may well be a horses-for-courses situation where the tube could prove to be quite useful, just in a different circuit.
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Old 31st March 2006, 06:28 PM   #16
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High perveance stuff.......Yes SY... quite right... It entered my mind...umm I honestly wouldn't recon my vendor would risk mucking me about with reflog line output stuff ...he knows I'm up in glass theory & MI & Hi Fi...unless his tester was pizzed drunk from weekend hangover.

Hitting the theory..The thought of grid blocking (bouncing of primary and sec electron emission from g1 can oppose grid current flow) can cause thyristor type latch up on certain tubes. I know it's mentioned somewhere in Langford Smith's book.

Ok....If the Jester sold me high perveance rebranded clown KT90's...line output apps wouldn't showup the problem I'm up against. That I'm pretty certain.
but as the grid leak in my amp circuits is 68K and driven from a slam low Z source, the remainder of the amp works pristine with KT88's right up to 40KHz....... the Ei KT90 data mentions direct substitute for KT88 and so on.....so what have
we got here ?

The conditions (quite normal).. 530V B+ UL43% (g2 knat's xck lower) via 220R carbon and quies set at 60mA. This implies g1 at approx -68V.... obviously peak signal swing around that figure.

However, as SY points out, checking at lower electrode voltages, there is the crossover characteristic with neg load lines. I've got a seeking suspicion we may have discovered the problem.

Uncovered a massive crummy manufacturing scandal ?

Any more revelations from the pit ?

richj
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Old 2nd April 2006, 01:38 AM   #17
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Default EI KT90 quality control....

...or lack thereof!

I bought 3 "match quads" of these from a vendor who recommended them over EH he also sold.
When I tested them they looked like they had just been selected at random!

Worse....using all 12 tubes I could not make one reasonably close quad...the best I could manage was two sort of OK pair!

Not counting 2 were duds right out of the box.

Of the working ten the weakest passed 78mA in my tester and the strongest just over 150mA....you could hardly believe they were even the same tube.

After 100 hours of use those two OK pair had drifted apart so far I had to go back to the others to make up a reasonable match again!

I've just had a similar experience with 2 so called matched quads of Chinese KT88s.

I've finally come to the conclusion that NOS tubes aren't overpriced after all because every modern power tube I have ever tried has had poor consistency.

John Corneille
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Old 2nd April 2006, 06:57 AM   #18
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oh yeah....I've also returned several KT90 octet sets to my vendor....there seems alot of duff ones going around.....reselling duff ones? I wonder what's going on behind our backs....

I know the pmcomponents group UK were thinking of a re-interest in KT90 production i.e drastically sorting the tube and it's problems out. I haven't communicated with the company for some time (last year) so I don't know what the up-to-date is.

I'm quite sure there would be a good market for KT90's if somebody could get them to work right. It remains a mystery as the tooling was Philips which was very reliable. It can't have all been bombed by NATO ?

richj.
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Old 2nd April 2006, 01:10 PM   #19
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It was hard getting a close match for two matched pairs out of the 5 pairs I own. Being able to set individual bias for each tube was the saving factor. Ran them in the Quicksilvers again with 485
VDC on the plate and 55mA each for bias with absolutely no problems.
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Old 19th May 2006, 04:37 PM   #20
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Quote:
Originally posted by burnedfingers
I have some EI brand KT90's and have used them in my Quicksilver mono block amps with no problems.

Those Ei Kt90. Are they any good to sub my JJ KT88?
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