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New kt88's or 6550

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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
 
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.
 
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.
 
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
 
May I put that in my signature?

Have at it.

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.
 
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.
 
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
 
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.

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.
 
tubelab.com said:


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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Snap !Must have purchased about same time..

I couldn't have done better if I tried. I still have about 20 of these tubes still new in the carton. I have used them to test ideas that I am not sure of. I have about 3 of them that I have banged on pretty hard over the years. They have survived for 10 years, so I guess that they were built right.

I don't put these things in any circuit where rare of expensive components are at risk, since I have seen them fry in some violent ways. I think the biggest bang I got was when a cathode bypass cap exploded after the tube shorted and the resistor opened.

Here is one of them being used in a clip lead test amp. This is a CCS loaded trioded KT88. The big sweep tube is the CCS and the OPT is isolated form DC by a big oil cap. Nothing expensive will blow if the tube shorts since the CCS keeps everything in line.
 

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tubelab.com said:

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.


Wondering if you've measured the output impedance, and perhaps peak power with the EH vs. other tubes.
Freq response as loaded by the speaker might also better demonstrate the differences. I'd expect more bass impact with higher output impedance actually since the LF rolloff Q will be higher.

I'm seriously interested in what gives the EHs better bass.

Pete B.
 
I have not tried EH KT-88, but I do have a set of SED KT-88s (then Svetlana). I ran them quite hard in an older amp and they survived just fine. I plan to try a pair in the SimpleSE biased good and hot once the chassis is done.

I can also vouch for the Tung-Sol 6550 reissues sounding nice (good bass on inefficient speakers), but I have only tried them in the Dynaco which doesn't push them very hard at all.

Russ
 
As far as current production tubes go my experiences with the EH output tubes has been very positive. Except for some 300B's I've used their tubes mostly in guitar amps, 6V6, 6L6, EL34, 6CA7,6550 and KT88 are the ones I've tried. The 6CA7 seems to be especially good and right now I'm using them in a Sovtek Mig 60 where I used to use the JJ E34L. They have a lot of headroom and they sound terrific in this amp. I want to try a set in my Hiwatt DR504 head too.

For what it's worth I have not cared for the EH small signal tubes but I've only used the 12AX7 and 12AY7 so I can't speak for all of them.

I do think there is some good stuff on the market if you're willing to give it a try.
 
wrenchone said:
I have a quad of Reflector 6550s lying about. Can anyone comment on their sonic characteristics? Their construction looks solid.

Ah ha....don't be fooled by the construction...The ill-fated Ei KT90 with a plum sized anode looks beefy enough, but on many just wrap the tube with a knuckle and the fireworks start on the innards. Tube amps sitting on top of bass bins looks good, not the right place for these tubes.

ps. A good and reliable substitute to the 12AX7 is the JJ ECC83S. The batch of 100 I had were remarkably consistent. Agree ?

richy
 
I have a quad of Reflector 6550s lying about.

There have been a lot of Reflector sourced tubes that contained the digits 6550 over the years. I used Sovtek 6550 WA in some of my monster guitar amps of years past. They worked very well in that respect, and held up well. I still have a few. They take a long time for the bias to stabilize (some are in the 5 to 10 minute range) but they have been used a lot. In fact these were my favorite tube until New Sensor lost my business and respect over some junk Sovtek 300B's. I did not use any New Sensor tube until I bought a box full of returns cheap and discovered the EH tubes.

They sound good in a Simple SE, but have less bass then the current production EH tubes and really don't like to eat 40 watts either. I have a set of vintage GE 6550's that have a much cleaner sound, but even less bass. Again these observations are with the Simple SE connected to 15 inch OB speakers. The EH tubes are cranked to 100 mA, the others at about 75 mA.

The picture changes when I connect my Yamaha NS-10's. All tubes have similar bass response since the speaker is the limiting factor, although KT88's and 6550's have noticibly more bass than EL34's or 6L6GC's.

The ill-fated Ei KT90 with a plum sized anode looks beefy enough, but on many just wrap the tube with a knuckle and the fireworks start on the innards.

Ditto the original Chinese KT88. It looks wicked until the fireworks start. You don't even need to thump them, they will fry all by themselves, but put them in a guitar amp that sits on top of the speaker and watch the light show. Wicked sounds come out of the speaker too!
 
I have a quad of EH KT90s that I bought years ago but never used. I went to put them into the ST70 recently after a JJ KT77 exploded and noticed one of the cathodes had slide down out of the top mica. I was able to smack it against my palm a few times and get it back into place. They all biased in fine after that and I put a few dozen hours on them before I finally got replacement JJ KT77s. They sounded good and gentle tapping didn't not move the cathodes. These were the tall, skinny ones that I believe are modified sweep tubes of some sort (PL509?). They sounded good and looked at home in the Dynaco.

Russ
 
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