Portrait of a tube

full index list

5690 - 5691- 6592

Jac van de Walle

These tubes have a bit of an unusual history. If it wasn't for Wernher von Braun, these tubes would not have existed. So I will devote some to him. It began in the early 1940's when the liquid fuel rocket motor was invented by Werner von Braun. I own a book written by him, in the 1950's, called in German (The way into space). I regards him one of the most brilliant engineers that ever lived. He was 100 years ahead of his time. The way he describes in 1950, how to go to the moon, how to go to Mars, use Skylab and the Space Shuttle. It is all in there, with calculations of all orbits, weight of the rockets, fuel weight, everything. He writes, costs will be high, but if a government wants it, it can be done. He describes in 1950, how a network of satellites, will make a pictured map of the whole earth, and how this will change the way of warfare. He says, the question is not if this will come, but when it will come.

Moreover he describes most NASA missions in this book, even those that are in the future still, are not described as futuristic. He describes these are real. How it's done, in detail, and what it will cost in terms of time and money. He writes about using a moon of Mars as landing station. He writes, these people will not be able to return. That will take place somewhere perhaps after 2040. Who knows. So far all his predictions have come true. That is what I call being ahead for your time. But....speaking of time.... he also has a history. He writes a few words about the V1, and V2, like how high they can fly, and how fast, and that's it. For him the V2 is where life begins. But for others it was where life ended. Also he forgets to mention his time with the SS and the NAZI's. So let's make up for this here.

After the war, he ran over to the USA with the major part of his staff, and a trainload of top secret documentation that he stole from his motherland. It was a matter days, before the Russians got there too. If the Russians would have been earlier, sure he would have become a communist heroe. Wernher von Braun was ranked "Sturmbannfuehrer" in Hitler's SS (very high rank). The SS was Hitler's elite troupes, with the death skulls and crossbones on their hat, and a licence to kill. So he deserved the same punishment as any other SS member. He used Jewish slaves to work in his factories, and what he was doing was not on "orders". He was a leading part of it.

Wernher von Braun and some other Nazis

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Anyway....these rockets work by a principle where very high acceleration gives them efficiency. Once they fire, acceleration pumps the fuel to the engines. They burn up all fuel in very short time, and then fly without engine for the rest of the trip, steering to the target using their instruments, like gyroscope, compass, speed and altitude meter. So there is a lot to control inside. In those days, even the best semiconductors were poor devices. Such as selenium rectifiers, crystal diodes, or experimental Germanium transistors, all of that does not meet requirements. Werner von Braun learned how to use magnetic amplifiers to control the V2, a perfect technology. It is almost forgotten these existed, even so today it is unknown how these were made, or how to design circuits around them. Only some raw devices are replicated today by tech nuts, but not those fine products of the past. With magnetic amplifiers they could build a complete, working radio receiver with speaker outputs. So no semiconductors, and no tubes. But the American Army went for electron tubes instead, and that was for a very good reason, and magnetic amplifiers are definitely subject to the EMP. (Elektro Magnetic Pulse) . There were three special tubes designated for use into rockets:

5690=rectifier
5691=high gain (similar to 6SL7)
5692 is medium gain (similar to 6SN7)

Wernher von Braun was in possession of full building plans of the V2 rocket, and the liberating forces got hold of a few unfired V2 rockets, and transported those to the USA. They were fired on the White Sands plains, USA, and still today this is a NASA test site. Here is how USA rocket technology began. The V2 was not designed to escape earth's gravity, as this cannot be done with a one-stage rocket. So it's a ballistic rocket, though it was capable of escaping the atmosphere and fly some time in vacuum. Which makes sense. because in vacuum they fly a lot further. These things could fly really far. The engine principle and the way it's engine was build, was a break through, and never changed ever since.

There is a good reason, why magnetic amplifiers and semiconductors could not be used for the next generation rockets. (The first was the Redstone rocket, build in Detroit). These rockets were made to carry nuclear bombs, and when such a bomb explodes, there is a huge Electro Magnetic impulse (EMP) , killing every semiconductor and magnetic amplifier in 500km distance. During the EMP itself, an electron tube will fail also, but after the pulse is gone, they recover and work normally again. So here you have the reason in a nutshell, why these three tubes were born.

What is so special about those? They were not made for long life, though we know their lifetime is excellent. They were made for low failure rate. The octal socket is known not to damage the tube pins in such way the tubes draw vacuum. Unlike modern Noval tubes that may loose sometimes vacuum in storage. So all together the choice was for these rugged tubes like 6SL7 and 6SN7 (what goes in is what comes out), in a modified form. So these rockets can be installed "ready to go" for 15 years, under the ground. Then when somebody presses the "go" button they must work instantaneously. Inside those tubes were many extras to ensure these extreme requirements. In literature, I find almost nothing about what is inside, but that makes sense, it was a war product. You can read here about the GE five star tubes, but that is a quality level much below that of the 5692.

Besides 5692 was rated for 500G shock, meaning if they drop them on the floor, and as long as the glass is not broken they should be still good. Try to imagine the force of 500G. For a short fraction, every piece part inside weighs 500x more than normal. To give you some idea what 500G does, the glass bulb of four gram weighs 2 kilograms, and may not break off the socket by that.

These three informations here was given to me by Kim Bond. Thank you Kim!

Important note about 5692 testing: This tube differs slightly from 6SN7, thought it is a replacement is almost any application. However, it cannot be tested accurately on any average 6SN7 tester. 5692 tester setting are DIFFERENT from 6SN7, no matter what the tube uncle tells you, do NOT buy 5692 that are tested in 6SN7 settings and come out good. They may just as well be not good. There is no work around, you HAVE TO USE 5692 settings. So any tester like Amplitrex 5692 or Russian L3-3 can be programmed for it.

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Link to datasheet here

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Another quality concept is the VT231. This is a military part number for a NAVY version of 6SN7. The older ones (most wanted version) have a chrome getter, and/or gray smoked glass.

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