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Old 31st March 2009, 02:33 PM   #1
nhuwar is offline nhuwar  United States
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Default New kt88's or 6550

So are all the kt88's and 6550 made these days all crap or are there some decent ones made.



I'm thinking about building a push pull amp with either but all I seem to hear is there junk.


Please give me you opinions????????????????????



Thanks,
Nick
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Old 31st March 2009, 02:47 PM   #2
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The KT-88 Genalex reissue is a really good tube. Honestly, I've found many of the people who criticize it have never heard it! Some of my far eastern customers say it's every bit as good - or maybe even better - compared to the originals.

The 6550C SED/Winged C is a good tube if it passes initial screening, but be aware they tend to be quite "hot" biasing.

The Tung-Sol reissue is a very good 6550 - but it's limited to about 35 watts dissipation in my experience, in kind of falls apart sonically above that.

The KT-88 EH is a good tube too, albeit it is a bit light in the bass. What's there is excellent, but I wish it had a bit more. This would be the tube I'd use in a bass-heavy system.

I've used all the tubes above in my Citation II amps, and I can recommend any of them. Are they as good as the best of the old stock? Other than the Genalex I'd say not quite - but they ARE as good as some of the old stock.
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Old 1st April 2009, 03:01 AM   #3
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When people say that they are junk, what does that mean? Do they mean that they sound bad, sound good but die early, or that they are junk because the earth's supply of magic mojo was depleted in the late sixties?

I don't know a whole lot about reliability, since I have not run any for any length of time. I do know that if you direct couple mosfets to the grid of triode wired Electro-Harmonix KT88s and drive it with a high power sine wave and try to get the plate voltage down to zero, they die in about two seconds. However, they sounded awesome right before I did that.

Genalex reissues sound really good. However, I haven't used them very much so again I can't comment on reliability. I'm setting them aside until I fix things not to kill tubes any more.
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Old 1st April 2009, 03:07 AM   #4
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Quote:
Originally posted by SpreadSpectrum
I do know that if you direct couple mosfets to the grid of triode wired Electro-Harmonix KT88s and drive it with a high power sine wave and try to get the plate voltage down to zero, they die in about two seconds. However, they sounded awesome right before I did that.

May I put that in my signature?
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Old 1st April 2009, 03:13 AM   #5
nhuwar is offline nhuwar  United States
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SpreadSpectrum,

I'm talking about just plain bad tube that fail quick or soon not sound wise. A friend of mine has had nothing but trouble with allot of the new 6550's and kt88. Now granted he is using them as pass tube so things are bound to be a bit different. I just want to buy some tube and not have to worry about the failing pre-maturely when ran properly.


Nick
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Old 1st April 2009, 03:25 AM   #6
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Quote:
May I put that in my signature?
Have at it.

Quote:
I'm talking about just plain bad tube that fail quick or soon not sound wise.
That's not been my experience with New Sensor tubes. I've only bought eight, but they worked fine. Until I killed the EH tubes, that is. I think Jim McShane offers some sort of warranty, if I am not mistaken. You might want to ask him about that.
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Old 1st April 2009, 03:42 AM   #7
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I run mine triode connected with 463V B+. I am impressed with these tubes as triodes. I think on the Sofia curve tracer website there are some curves of various tubes. The 300B and KT88 triode curves are plotted on the same scale, so you can do a good comparison between the two tubes by just flipping back and forth in picture viewer. The 300B curves look a little nicer, particularly in the higher voltage-lower current area of the curves, but the KT88s are way cheaper than 300Bs and have a higher mu, and if I'm not mistaken miller capacitance still comes out quite a bit lower, too. rp is pretty nice, too.
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Old 1st April 2009, 01:36 PM   #8
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The new issue TungSol 6550's I put in my amp a year ago,(currently 2000 hrs at 450V+) and consistently running near the diss limit barely budged a mA from quiescent the day after I put'em in. I agree with Jim's sonic comments not to go above 35W dissipation and keep with a low value grid bias resistor. On this issue I've never seen a spec sheet for the New issue TungSol 6550 and I presume it's sim to the A NOS version.

I find the Svetlana range, sounding just as punchy and reliable, somewhat more heater sensitive and taking longer to settle down.

Fair to say, a near decade ago when the F.E was producing clone production , the en masse reputation was awful and wasn't unusal for a new tube to flair-up within hours to being useless. But now gladly QA has changed for the better. There are some excellent clones around; get your vendor to run them in.
I haven't come across any clone non-Russian 6C33; now those I would be very fussy over. Perhaps others have experience of.

richy
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Old 1st April 2009, 01:55 PM   #9
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Quote:
The KT-88 EH is a good tube too, albeit it is a bit light in the bass. What's there is excellent, but I wish it had a bit more.
I tend to agree with the opinion that the EH KT88 is a good tube. As for the bass, every tube will interact with the entire audio system in a different way. I am using a Simple SE connected up to 15 inch Silver Iris speakers in open baffle cabinets made from 40's vintage console radios. The EH KT 88's in UL with some cathode feedback to lower the output impedance make the most powerful bass that I have ever heard come from a single ended amp. I run them hot at about 400 volts across the tube and 100 mA of current. The bass can be heard inside the house across the street. It is solid and not boomy. I have tried a bunch of other tubes in the same system and some give more detail, but none rock the house like the EH KT88.

Quote:
Fair to say, a near decade ago when the F.E was producing clone production , the en masse reputation was awful and wasn't unusal for a new tube to flair-up within hours
I bought a box of Chinese made KT88's cheap about 10 years ago from a tube vendor who refused to carry them any more. These things remind you that the Chinese invented fireworks! They will spark out big time at 400 volts and 50 mA in a guitar amp. I was using them for 30 WPC stereos at 360 volts and even then they would randomly fry. They will red plate at 25 watts.

The new production Shuguangs or Valve Arts seem to take some serious abuse, but the bass is nothing like the EH tubes.
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Old 1st April 2009, 03:25 PM   #10
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Quote:
Originally posted by tubelab.com


I bought a box of Chinese made KT88's cheap about 10 years ago from a tube vendor who refused to carry them any more. These things remind you that the Chinese invented fireworks! They will spark out big time at 400 volts and 50 mA in a guitar amp. I was using them for 30 WPC stereos at 360 volts and even then they would randomly fry. They will red plate at 25 watts.


Snap !Must have purchased about same time..
The tube in pic also destroyed the o/p tranny. Don't let this happen to you.

richy
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