Tube specs info?

[tennisets]

Well, I just bought a NOS Raytheon 5751 tube ($25) for my Mg Head, and it sounds great! However, I have a couple of questions. First, I am curious as to the production date, quality, etc. of this tube. On the side of the tube it says this:

40
280
63-40

and it also says:

JAN-CRP-5751

What does all of this mean? I gather the JAN-CRP-5751 must be the part number, but what is the other stuff? Would someone please clue me in?

Also, I've seen a couple of these on ebay, and they say "windmill getter" or "halo getter." What does that mean? How can I tell what mine is (no original box)? Thanks for the help!

 

[tennisets]

Okay, I read a couple of things I found on google (one by Nick Dangerous on tuberolling the MG Head). I didn't realize how well received this tube has been! I guess I just got lucky... At the audio store they had a couple of other 5751s, but "Raytheon" seemed to sort of ring a bell. I guess I must of seen something about it somewhere.

But I still don't know how to find out what year this tube is, and some other things about tubes confuse me. Here are my questions:

1) What does JAN mean?
2) Why are NOS tubes so much more desirable/better?
3) Assuming the answer to 2 is that they were made better and are better quality during the "tube era", why does no one make good tubes anymore?
4) What happens when the supply of NOS tubes runs out (I know that will take a loooong time, but it's interesting to think about)?

 

[mkmelt]

40
Might be the production run number.

280
I think this is the batch number

63-40
This is the Date code. The tube was manufactured in the 40th week of 1963

JAN-CRP-5751

JAN is short for Joint Army Navy. These tubes were manufactured for the US military. As such they had to be especially rugged and have very high quality control. That does not mean they automatically will sound superior, just that they are well made tubes.

1) What does JAN mean?
See above

2) Why are NOS tubes so much more desirable/better?
They last a long time in actual use. Many NOS tubes have a unique sound that is highly sough after.

3) Assuming the answer to 2 is that they were made better and are better quality during the "tube era", why does no one make good tubes anymore?
There are some good sounding tubes made today in the former Soviet Union (Sovtek, Electo Harmonix premium brand). They may not last as long as a NOS tube because the vacuum inside the tube is not as good, they don't take the time to pump out all of the air that would make a longer lasting tube.

4) What happens when the supply of NOS tubes runs out (I know that will take a loooong time, but it's interesting to think about)?
As long as their are electric guitars there will be a demand for tubes for tube guitar amplifiers. The more common small tubes such as 12AX7, 12AU7, 5751 will continue to be made, the less common ones will become increasingly rare until the price of a single tube makes it impractical for the average person to restore a vintage piece. In the case of output tubes, when the supply runs out, if there is a similar replacement tube being made then people will have the option of changing the tube sockets on their amplifiers to use the substitutes that are still available. One example, the 7868 tube used in some amplifiers including the Fisher 400 receiver is no longer made. The 7591 tube is an equivalent tube with a different base and pin configuration. If you replace the tube sockets in the Fisher 400 with tube sockets for 7591 tubes and rewire for this tube, you can use the 7591 in the Fisher. (It might be a tight fit as they 7591 are a bit fatter due to the base structure of the tube.)

 

[tennisets]

Thanks, that was really interesting! Incidentally, the Raytheon seems to have been a very good choice. IIIIII like it!

 

[mkmelt]

The getter is a structure inside the tube. When the tube is manufactured, there is still some O2 gas molecules floating around inside even after the vacuum process. The getter flashes one time, like a photo flash bulb (please don't ask what a flash bulb is, it will make me feel old), the first time the tube is powered up. This causes any free O2 to bind with the getter flash coating and the tube will then have what is usually a very long life. The getter has nothing to do with the signal produced by the tube, it is just a convenient way to identify who manufactured a given tube since many times tubes were rebranded and sold under a different label.

Getters are shaped into different configurations such as circles, squares, and disks. Some tubes have the getter mounted on top, other times on the side, sometimes both if the tube is large. The windmill getter looks like a windmill or a propeller.

http://www.buybeach.com/tubes/5751_rtn_westinghouse.htm

If your tube has this type of getter, then it is a windmill getter Raytheon. This tube was manufactured by Raytheon, even though it is labeled Westinghouse. No other manufacturer used this getter style in a 5751 tube.

You can ask this seller if he has any more, but in the past he has been sold out of this tube. The Raytheon 5751 with the windmill shaped getter sounds very good in some amplifiers, but only average to below average in other uses. So unless you know that this tube works well in your particular amplifier, don't assume it will be a match made in heaven in your amp. It happens to work very well in the Fisher 400 and the MG Head amplifier.

 

[tom hankins]

Quote:

Originally Posted by mkmelt 40 Might be the production run number. 280 I think this is the batch number 63-40 This is the Date code. The tube was manufactured in the 40th week of 1963 JAN-CRP-5751 JAN is short for Joint Army Navy. These tubes were manufactured for the US military. As such they had to be especially rugged and have very high quality control. That does not mean they automatically will sound superior, just that they are well made tubes. 1) What does JAN mean? See above 2) Why are NOS tubes so much more desirable/better? They last a long time in actual use. Many NOS tubes have a unique sound that is highly sough after. 3) Assuming the answer to 2 is that they were made better and are better quality during the "tube era", why does no one make good tubes anymore? There are some good sounding tubes made today in the former Soviet Union (Sovtek, Electo Harmonix premium brand). They may not last as long as a NOS tube because the vacuum inside the tube is not as good, they don't take the time to pump out all of the air that would make a longer lasting tube. 4) What happens when the supply of NOS tubes runs out (I know that will take a loooong time, but it's interesting to think about)? As long as their are electric guitars there will be a demand for tubes for tube guitar amplifiers. The more common small tubes such as 12AX7, 12AU7, 5751 will continue to be made, the less common ones will become increasingly rare until the price of a single tube makes it impractical for the average person to restore a vintage piece. In the case of output tubes, when the supply runs out, if there is a similar replacement tube being made then people will have the option of changing the tube sockets on their amplifiers to use the substitutes that are still available. One example, the 7868 tube used in some amplifiers including the Fisher 400 receiver is no longer made. The 7591 tube is an equivalent tube with a different base and pin configuration. If you replace the tube sockets in the Fisher 400 with tube sockets for 7591 tubes and rewire for this tube, you can use the 7591 in the Fisher. (It might be a tight fit as they 7591 are a bit fatter due to the base structure of the tube.)

I'm sure you have been told this before, but....
Your knowledge and informative posts never cease to amaze me. I learn something useful from every post you write. Thank you.

 

[Hirsch]

Just to add a footnote "CRP" indicates a Raytheon tube. "CRC" = RCA, "CHS" = Sylvania, "CKR" = Ken Rad, and so on.

 

[tennisets]

Thanks guys, that tought me a lot! I have a windmill getter Raytheon 5751 and I'm using it in my MG Head, so I guess it's no wonder it sounds so good

. I just can't get enough of this HD-600/MG Head combo.

 

[kevin gilmore]

quote
The getter flashes one time, like a photo flash bulb (please don't ask what a flash bulb is, it will make me feel old), the first time the tube is powered up.

NO that is not how a getter works. The getter is inductively heated by
a 5 to 15mhz rf supply till it gets red hot. Then it expels the chemical
inside the top of the tube. This is done at the factory. For really rare
tubes you cannot find any other way, a gassy tube can typically be
reflashed at least one more time.

 

[mkmelt]

"The getter is inductively heated by a 5 to 15mhz rf supply till it gets red hot. Then it expels the chemical inside the top of the tube. This is done at the factory."

Well Kevin that may be true if you happen to have access to enough plutonium to produce the 1.21 Jigawatts of electricity necessary for a flux capacitor to operate, but I managed to cause the getter to flash in a NOS 12AX7A tube made in India in the 1980s just by plugging it into my lowly EMC-213 tube tester. After the flash, when my heart started beating again, I noticed a shiny coating was visible all around the inside of the top of this tube whereas before it had been clear. It seems that this particular tube was not flashed at the factory.

As far as I have ever heard or read, a getter will flash only once. It is true that as the tube gets used up, impurities burned off of the coating on the cathode, grid, and plate surfaces may be trapped by the remaining getter flash material. In this way very old and well used tubes appear to lose some or most of their getter flash coating. This is one, not particularly accurate, way to judge how much life remains in a given tube.