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Author Topic: 3-500Z Amperex tube  (Read 4927 times)
K4RVN
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« on: April 01, 2010, 09:42:12 PM »

I have stored my 10 year old 3-500Z Amperex tube for
almost a year now in the upright position. It had full output, but I bought a new tube made in china for a spare and have been very happy with it so far.
Now that the warranty on my new tube is about to expire, I thought of putting the Amperex back in my Al80A because I don't know how long it can be stored without damage to it. Would someone be kind enough to
comment on how long a 3-500Z could be stored? Thanks for any comments

Frank
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K0CWO
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« Reply #1 on: April 01, 2010, 10:56:45 PM »

Frank,

The shelf life of glass tubes is a much debated topic.  I'm far from a subject matter expert, but from what I have read if you have glass backup tubes, it is wise to rotate them on an annual basis to ensure a proper seal.  I recently acquired a nine year old twin 3-500 amplifier which had not been used for several years. Apparently one of the tubes experienced a flash over due to the fact that oxygen entered the vacuum, commonly referred to as a "gassy" tube. When it comes to "gassy" tubes, 3-500 tubes have a getter compound attached to the plate of the tube that allows elimination of this "gas" when the tube reaches a certain operating temperature. How to prevent this gas from doing damage to the tube or amplifier when a potential flash over occurs is another much debated topic.  Amateur operators, some of them engineers much smarter than I am, will recommend different methods of "waking up" glass tubes that have been stored for an undetermined amount of time.  There is lots of information available on the web that will give you different points of view on this subject.  The most popular approach will instruct you to install a tube that has been stored for a relatively long time and let it "cook" on filament voltage without applying any plate current for 12 hours or so.  Those who recommend this procedure must imply that the getter material attached to the plate will remove the gas following this break in method.  Other smart amateurs argue that filament voltage alone will not bring the operating temperature up enough for the getter compound remove the gas, hence not preventing a flash over in the tube.  Who is right or what method of break-in is better is a matter of conjecture or theory as far as I’m concerned. I am not smart enough to give you a definite answer on this issue.

From experience, I think it is wise to:  rotate glass tubes on an annual basis; whether needed or not let them warm up by applying filament voltage for 12 hours or so after which you use the tube up to maximum design specification in order to heat the tube so that the getter compound can remove what it was designed to remove.

Having made a long story, long to late, I acquired a 17 year old AL-80A with an Eimac 3-500Z that had not been run regularly for 10 years or longer.  I plugged this amp in like a new amplifier and tuned it for maximum output without any issues whatsoever.  

Moral of the story?  The light bulb either works, or it doesn’t.

73, BJ
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K4RVN
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« Reply #2 on: April 02, 2010, 08:15:32 AM »

Thanks for comments BJ. I think I will install the amperex again to rotate the tubes as you mentioned.
I'll let it sit overnight with the filament also and no HV whether it does any good or not.

Frank
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W8JI
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« Reply #3 on: April 02, 2010, 09:18:26 AM »

Thanks for comments BJ. I think I will install the amperex again to rotate the tubes as you mentioned.
I'll let it sit overnight with the filament also and no HV whether it does any good or not.

Frank

Frank,

You can let the filament run til the cows come home and it will not help.

The gettering agent in the 3-500Z is zirconium, and it is coated on the anode, NOT the filament.

If you don't want to take my word for it you can look on Internet, but zirconium catalyzes most common gasses optimally at 1000 degrees C or slightly hotter. 1000 degrees C takes about 300 watts of anode dissipation, and would be a bright red color on the anode. The anode has to be at least 500C for the zirconium to have any effect, and that is a faint black red color.

Running the filaments is a waste of time. Anode heat is what absorbs gas.

http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm


73 Tom

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K4RVN
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« Reply #4 on: April 02, 2010, 03:16:27 PM »

Tom,
I believe you. I have read the same elsewhere about it taking high voltage. I will do it anyway like I said whether it helps or not.
Thanks for your comments as I was hoping to hear a post from you on this subject.I have come to listen when you write. Half the time or more I don't know what you are talking about, but I believe that you do.
Thanks,

Frank
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NJ3U
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« Reply #5 on: April 06, 2010, 06:28:12 AM »

I found the Eimac Care and Feeding of Tubes series to be very informative. You can download a free 6 part set @ http://www.cpii.com/library.cfm/9

73
KC2UML
Rory
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K4RVN
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« Reply #6 on: April 06, 2010, 11:18:36 AM »

Rory,
I did scan the site, but found nothing about the 3-500Z or similar glass envelope tubes. Did you happen to see anything? Thanks for the comment.

Frank
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K2TY
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« Reply #7 on: April 06, 2010, 12:48:13 PM »

Tom in the link provided, you mention that 811s and 572s like 3-500s use a zirconium gettering material on the plate. Some time ago I was engaged in a debate regarding this very subject. I made the statement that running those three tubes with filament voltage and no anode caps would not be helpful for gettering the tubes. Did I put my foot in my mouth? The 'EE' I was speaking with was adamant that 811s and 572s should be operated with filament voltage only for a few hours.

I see contradictory statements at RF Parts:

"The Svetlana 572B..... Temperature-initiated titanium "getter" material is permanently embedded in the surface of the rugged graphite anode for superior gas absorption. This improved "getter" system operates continuously AT HIGH TEMPERATURE, and is over six times more effective than flash getters silvered on tube's glass envelope." -http://www.rfparts.com/tubesvet.html

"Transmitting tubes generally require a "burn in" time to increase emission to its nominal value. In broadcast stations, 1-3 hours at rated filament voltage is allowed for burn in. This initial operation allows the GETTERS, materials which absorb and hold residual gas, to finish the vacuum of the tube in its final operating environment. In an Amateur Radio amplifier, tubes will sometimes require 50-200 hours of accumulated "key down" transmit time to remove the residual gas and condition the filament for full emission. It is well advised to allow tubes to operate in standby mode (filaments on, no TRANSMIT) for 2-3 hours before tune-up.

The 811A, 572B, 3-500Z, 4-400, etc. utilize a thoriated tungsten filament, which is highly dependent upon sufficient filament temperature to provide adequate electron emission for normal operation. Emission increases as the thorium migrates towards the surface of the filament wire. This is why it is recommended to "burn in" these tubes before operation." - http://www.rfparts.com/tubeapp.html

Is that second quote paragraph poorly worded?
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W8JI
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« Reply #8 on: April 06, 2010, 03:42:45 PM »

Tom in the link provided, you mention that 811s and 572s like 3-500s use a zirconium gettering material on the plate. Some time ago I was engaged in a debate regarding this very subject. I made the statement that running those three tubes with filament voltage and no anode caps would not be helpful for gettering the tubes. Did I put my foot in my mouth? The 'EE' I was speaking with was adamant that 811s and 572s should be operated with filament voltage only for a few hours.

You can hurt the filament if it runs many days without emission, not hours.

Quote
I see contradictory statements at RF Parts:

"The Svetlana 572B..... Temperature-initiated titanium "getter" material is permanently embedded in the surface of the rugged graphite anode for superior gas absorption. This improved "getter" system operates continuously AT HIGH TEMPERATURE, and is over six times more effective than flash getters silvered on tube's glass envelope." -http://www.rfparts.com/tubesvet.html


I guess from that Svetlana changed to titanium, which is about like zirconium. Very few high power transmitting tubes ever used flashed getters so that "six times more effective than flashed getters" is mostly marketing hyperbole. It still has to be very hot to getter the tube.

Quote
"Transmitting tubes generally require a "burn in" time to increase emission to its nominal value. In broadcast stations, 1-3 hours at rated filament voltage is allowed for burn in. This initial operation allows the GETTERS, materials which absorb and hold residual gas, to finish the vacuum of the tube in its final operating environment. In an Amateur Radio amplifier, tubes will sometimes require 50-200 hours of accumulated "key down" transmit time to remove the residual gas and condition the filament for full emission. It is well advised to allow tubes to operate in standby mode (filaments on, no TRANSMIT) for 2-3 hours before tune-up.

This is a practice that is rumored to help emission (NOT gas) but I've never seen it work. Not ever. We received a batch of low emission 3CX1200's once and Eimac had us cook the tube filaments at 9 volts or more (I can't remember exactly) for a half hour to an hour, and then run the filament at normal temps overnight. After that the emission was up. About 20 minutes later though, the emission was gone again. I had the same thing happen with 811's some time later.

This problem occurred because the filament surface is not properly "aged" after being manufactured or was manufactured wrong, so emission was low.

Quote
The 811A, 572B, 3-500Z, 4-400, etc. utilize a thoriated tungsten filament, which is highly dependent upon sufficient filament temperature to provide adequate electron emission for normal operation. Emission increases as the thorium migrates toward the surface of the filament wire. This is why it is recommended to "burn in" these tubes before operation." - http://www.rfparts.com/tubeapp.html

So it actually appears they agree with what I have been saying, it is NOT a gettering process. It is a emission restoration process, and what they are saying is the tube filament was not cooked in properly at the factory and we need to finish the job for the manufacturer.

The typical manufacturing process would be to heat or flash the filament for just a few moments at a very hot 2500-2800K. After that the filament is aged at 2200K (this is what Eimac had us try) for some minutes to an hour. Then they had us run the filaments at normal voltage overnight (I'm not sure why, except the 3CX1200 being a ceramic external anode tube does getter from the filament heat, and maybe they thought the elevated filament temperatures might have released gas).

I was never successful in the long term restoring emission this way. Probably because I was only doing the later steps when the first step was not done properly.

This has nothing to do with gas or with the tube sitting unused. It is an emission issue.

Degassing of a 811 or 3-500 or 572 would occur only if the tubes is arced internally at very low arc currents, or has the anode heated at least to a very dull red color.

73 Tom
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WX7G
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« Reply #9 on: April 06, 2010, 05:42:18 PM »

The 811A tubes in my amp have barium getters near the base. One wasn't even flashed.
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W8JI
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« Reply #10 on: April 07, 2010, 02:50:16 AM »

The 811A tubes in my amp have barium getters near the base. One wasn't even flashed.

You're right, different 811's can be different but none of them that I have ever seen getter from the filament heat.
« Last Edit: April 07, 2010, 02:52:16 AM by Tom Rauch » Logged
KJ6QVB
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« Reply #11 on: December 01, 2012, 06:07:53 PM »

I am in a similiar situation, rebuilding a Heathit SB-220 and I purchased (2) NOS Eimac 3-500Z tubes about a year ago and now I want to install them in the amp. Not sure how long they sat before I bought them, maybe a year or two. Should I let them cook on filaments alone for a few hours before I apply exciter RF? Feeding the amp with an HW-101 and out to a Comet CHV-5x which is only rated for 150W means I cannot bring the 500Zs up to max and really redden the anodes. Suggestions? Low power for extended periods not to exceed the output duty hrs of the HW-101?
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W1QJ
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« Reply #12 on: December 01, 2012, 09:27:56 PM »

You have 2 problems to deal with.  Without some sort of measure ot test the tubes for gas you can either plan for the operation or take pot luck.  Running the filaments only will do no good to de gas a gassy tube(s).   your tubes are either gassy or they are not.  You can put them in the amp and turn the amp on  and see what happens.   If the tubes are gassy you will find out soon enough but you will have to accept whatever might happen.  Depending on the gassy intensity will determine what might happen.  The alternative is to bring the amp up slowly on a variac and observe signs of gas.  Again, depending on the intensity of the gas will determine how soon you will see signs.  A badly gassy tube brought up slowly on a variac  may save you some amp damage considering the alternative.  I NEVER INSTALL TUBES OF UNKNOW QUALITY AND JUST TURN AN AMP ON.  Your second problem is not having an antenna to handle the power.  The amp will not operate properly at only 150 watts output don't even attempt it.  Get an antenna that can handle the power and get a dummy load too.
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G3RZP
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« Reply #13 on: December 02, 2012, 03:47:56 AM »

When the English Electric Valve Co started manufacturing 813s just after WW2, they had a problem with very short life before the emission failed. That turned out to be low thorium content in the filament wire.

Running at over voltage for bit brings the emission up - sometimes temporarily, as Tom found but occasionally permanently.
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