Features[ edit ] The KT88 fits a standard eight-pin octal socket and has similar pinout and applications as the 6L6 and EL Specifically designed for audio amplification, the KT88 has similar ratings to the American which was designed for use as a servo amplifier. It is one of the largest tubes in its class and can handle significantly higher plate voltages than similar tubes, up to volts. A KT88 push-pull pair in class AB1 fixed bias is capable of watts of output with 2. The transmitting tubes TT21 and TT22 have almost identical transfer characteristics to KT88 but a different pinout, and by virtue of their anode being connected to the top cap have a higher plate voltage rating 1. It was manufactured in the U.
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And no, it is not as easy as you would like, because a bad getter indicates a defective tube. That is why getterology is of little use for most people. This becomes particularly clear, when tubes with obviously defective getters are praised on Ebay as excellent working, and both seller and buyer do not notice the bad getter, indicating the end is near.
Strangely, there is no interest for this, though it is clear to see by the getter often, the tubes are rubbish. More difficult is also the reverse situation: The getter looks fine also to me and when you test such tubes, they are rubbish. Here, the biggest mistake of all is made: Many think, a fine looking getter is the same as a fine working tube.
This is simply not so. So in short: A good getter means not the tubes are good. A bad getter means the tubes are bad, also when the optical situation look so nice for the rest of it. On the left picture you see a tube that was for sale an auction website. It is clearly visible that this getter has gray edges. Also some part of the getter is gone. On this picture you see two working, used tubes that were offered on Ebay, for very high prices. The left tube getter looks fine.
The right tube has some of the getter edges gone as well, and the GEC stamp is badly burned. These are the brown type of getters, at the end of lifetime these start to develop concentric rings, of some blue-gray color and after more use, the edges begin to disappear. As a next step, the tube gets gassy, without the getter being white. At this moment of Ebay sales, they probably test still good. I was send this picture by someone who found those on Ebay, and who was afraid they were fakes.
Well, yes they are fakes. Inside is the Chinese KT88 system clearly visible. What is even worse about these, they were offered as NOS, and they are in the box with a bad vacuum getter. You can see the gray ring around the getter. With all getters, the edges are thinner than the middle part. So once you see the edges are no metallic looking anymore, this means some part of the getter has been used up.
This kind of getter wear out comes from use. This is not air leaking to the inside, but this is plate out gassing which causes this coloring. The print However, is clean, not burned. So this is a real bad case, old worn out Chinese tubes were cleaned, re branded and re boxed as Genalex. Conclusions with those Gold Lion tubes: A great part of the lifetime is gone. Marking is faked. Inside is no Genalex KT Here is a typical worn out getter. Here is the same kind of getter, but still good.
Thanks Bernardo! The text is: The Genalex Power Output tubes in these cartons have been matched to each other on the finest test equipment available. The company is B. This is how the B. C tubes look like. The sticker is a bit different from most others, but it is genuine, and inside is a genuine GEC tube. Note: Be careful, this sticker is being perfectly faked by the Chinese at the moment.
So by itself this sticker means nothing anymore. These days are over. You can only trust the tube inside piece parts. Above you see the test limits for the KT This is historical rare information. Note however, these certificates do NOT represent actual test data of the tubes in any way whatsoever. Though they do a great job in giving you that impression. What is hand-written in there, is nothing but general information, and NOT related to the individual tubes inside the boxes.
If you have of those certificates, they are all the same. So on the one hand it is good they provided that information, at least they say the tubes comply with something.
So you know how to check them, and you can say if they are good or not. I find this is a y way to the owner, by giving the impression this hand written data was collected. If you are skilled with datasheets, and read these certificates carefully, you will see this is just hand written information which is copied from the standard datasheet. It is fine when the tubes comply with that, but if not they would have been rejects anyway.
So this test certificate is plain bullshit. Made for amateurs that think many numbers are many good. It is just the so called test data is for the birds. You need to know a few things here. The MO Valve company is not existing anymore. That is all they own. They do not use the original tools, neither are their new tools copies of the original tools. Which for me is not a real KT You can think of this what you want, and you should. The boxes and printing, and optics are perfect quality.
Better than the tubes itself. I have sold the New Sensor for some years, and I was extremely disappointed by the tubes, as well as refusal to serve guarantee. Dealers get there only 90 days after receival. So when they store the tubes for 90 days, they can sell to the end customer for whatever the conditions are, but the dealer itself gets no guarantee when there is something wrong. The ones I had, showed all the typical errors, KT88 can have.
That is: Heater-to-grid shorts, after postal transport. Is the post to blame or the factory? All I know is, they damage too quickly. Another problem, the most occurring I had, was vacuum problems. The getters get bad edges at first, and emission seems lower. Though many times the tubes still work, I do not trust such tubes. Another problem I saw often, was screen grid current is too high, this over-heats the screen gird, the carbon layer evaporates , this damages the whole tube. They short in the end, blowing out the amplifier fuses.
Quality is the same medium level. They were fine when I received them, but sometimes tubes can be on stock for a few years, and I had several that developed gas. What specifications? Today, many manufacturers blow a cloud of smoke around the question, how tubes should be checked for quality. For a serious tube dealer, trying to do a good job, this becomes a problem, as he has no way to do incoming inspection.
So problems can get passed on to the buyers before you know it. Interesting, on those historical certificates, the acceptance limits are there indeed. For instance Plate Current is between and mA. With that information, your tube dealer can test what is a good tube, and what is a reject. After many rounds of discussions, I got the following answer from J.
Morrison by phone, who was at that time the chief technical engineer of New Sensor New York. We will not supply acceptance level data. The tubes are good. We sell most tubes into the guitar amplifier market. The HiFi market is only a few percent of our sales anyway. We can easily do without those nasty HiFi customers if we have to.
I am sorry but this is how things are. Later, I met J. Morrisson on some occasions, and I really have to say he is such a wonderful and inspiring person. I removed this brand from my sales program. Not any better than Electro Harmonix which costs only half.
The KT88 / KT66 /6550 Directory