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Author Topic: New 3-500ZG Tubes / Do you need to break in?  (Read 1148 times)
KB4MUV
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« on: October 14, 2009, 01:58:59 PM »

I have a Heathkit SB-220 that was in storage for several years.  When I turned it on, it appears one or both tubes were gassy and that took out several other componets.  Well we have rebuilt her and she appears to be good to go.  Now I have ordered 2 brand new 3-500ZG tubes from RF Parts to install.

Now my question is, what do I need to do to break in these tubes if anything?Huh?

I understand I should whipe down the globes with alcohol swabs to get figerprints off to prevent hot spots.

But I have also heard I should run them without the anodes attached for 24 hours and other assorted stuff to break them in.  

I have retubed radios before, but never an amplifier with these type of tubes.  This beast has taught be so much!!!!  Ha!  Ha!

What might the words of wisdom be on this endeavor?Huh?

Thanks in advance for any information.

Ken
KB4MUV
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W1QJ
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« Reply #1 on: October 14, 2009, 02:34:59 PM »

New tubes are usually gettered from the factory and do not require any special treatment.  I have bought numerous tubes from RF Parts and I just installed them and away I went.  Never had a problem.  Usually the .82 grid resistors blow out when a gassy tube flashes over.  I have the OEM replacement resistors for that if you need any.  73 Lou
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K6AER
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« Reply #2 on: October 14, 2009, 02:35:18 PM »

Plug the tubes in and turn the amplifier on. The  Thoriated Tungsten filaments are ready to go as soon as they glow.

Older glass tubes can become gassy, that is oxygen migration into the tubes via the metal base pins and some times you will have a high voltage flash over. The good news if you do have flash over it will generally dissipate any oxygen that has leaked into the tube. Bad news it may take out a anode or cathode resistor.

The only way you can getter the tube is to have the anode heated up from use. The filaments lighted is not enough heat to getter the tube.

Do some reading on Tom’s web site at W8JI. He has a boat load if information out there.
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K4TLJ
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« Reply #3 on: October 14, 2009, 02:50:04 PM »

Just a wild idea from a new guy...

Has anyone ever tried using a large magnifying glass to focus sunlight onto the anode to heat the anode and getter the tube without applying HV?
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K6AER
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« Reply #4 on: October 14, 2009, 03:51:20 PM »

I think the amplifier heating the tubes in actual  operation might be much easier.

News Item just in from MSNBC:

“A Ham today collapsed from heat stroke today while trying to heat a tube with out electricity. The older ham was scene holding a gigantic 42” magnifying glass over the little tube from an unknown piece of equipment.  Just as the John Q. Ham collapsed, the magnifying glass rolled down the driveway and came to rest against a tree. The tree caught fire setting 60 acres ablaze. The Pounduk Fire department was able to put out the blasé in just under 2 hours.

John Q. Ham said he had insurance from the ARRL but the ARRL spokes person was not available for comment if this was covered under the ham umbrella policy.

It is unknown if this new method of making tubes glow is considered a green technology but Al Gore (Ex Vice President to Clinton) will be giving a series of lectures at Dayton ham convention next year on how this magnifying glass technology will produce thousand of jobs in the linear amplifier industry. At this point, night time technology is still years away from general ham tube heating use.

An unnamed spokesperson for PETA felt this technology is not with out risk for it is rumored several moles were displaced from the filed fire”
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KB4MUV
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« Reply #5 on: October 14, 2009, 03:59:40 PM »

Thanks Lou for your reply and offer...  I have some spares.  I did go ahead and replace the whole board.  And had ordered some of the res.  

Ken
KB4MUV
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KB4MUV
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« Reply #6 on: October 14, 2009, 04:03:30 PM »

Thanks K6AER for the info on the website...  I will go there and see what they have....

Yeah the ole tubes were gassy and beyond saving.  And figured that looking on eBay wasn't the route to go to replace them.

Ken
KB4MUV
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WB2WIK
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« Reply #7 on: October 14, 2009, 04:33:42 PM »

3-500ZGs don't require any special burn-in time.

Using them until the anodes glow red/orange is what keeps them gas-free.  This is one tube design that lasts longer when frequently used than it does "on the shelf."

Not all tubes are like that, but this one is.

Although I do keep "spares" around, I rotate the spares through an active amplifier at least once a year so the spares on the shelf were always recently used.  Buying new spares and letting them just sit on the shelf isn't a good idea.

WB2WIK/6
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K4DPK
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« Reply #8 on: October 14, 2009, 06:24:15 PM »

Mike you are a trip!

Phil C. Sr.
k4dpk
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K4TLJ
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« Reply #9 on: October 14, 2009, 07:24:50 PM »

Well at least my suggestion brought out the latent satirist on the forum. Smiley
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KA3DNR
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« Reply #10 on: October 16, 2009, 06:14:35 PM »

That was funny Mike...
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KM3F
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« Reply #11 on: October 17, 2009, 12:23:45 PM »

For use in a modern amplifier such as the AL80B, I would begin a new tube with about 3 hours of filiment only, then low RF drive, then more drive to bring the plate current up in the 400-500 ma range watching the plate/s for color. A bright orange is about 900°f.
Do this several times to be sure there are no issues.
I know the tubes are 'supposed' to be ready to go but you have no idea what you have when you get them. Better to be cautious than fool hardy if a little gass is still ungettered and causes a flashover.
In the case of the 80B with it's auto bias circuit, a flashover can damage the auto bias circuit.
Been there already and the manuel tells you the same thing.
Another item is filiment over voltage can out gas it's material. Look at your input line level especially on 240 ac and adjust taps to get the filiments at or near the correct operating voltage.
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KB4MUV
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« Reply #12 on: October 17, 2009, 02:55:20 PM »

Thanks guys for the information.  I called Tech support at RF Parts and they said just let them run for 6 - 8 hours in the amp prior to applying an RF.  And then go easy until I make sure everything holds together....  

Well she is back together and doing just that.  Everything seems to be fine.  I hope!  

Again guys thanks for taking the time to respond.  You advise will be well taken.

Ken
KB4MUV
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WX7G
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« Reply #13 on: October 19, 2009, 06:43:18 AM »

no
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W8JI
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« Reply #14 on: October 19, 2009, 06:33:31 PM »

Despite what people seem to think there is virtually no gettering or aging that occurs through running a 3-500Z filament without significant anode current. A long filament run time with no emission can help emission upon application of HV, but very quickly that emission will go away again if the tube filament was not properly aged. The end effect is there is no gain from just using the tube from a cold start.

The zirconium gettering material on the anode activates at fairly high temperatures. Some gettering would take place if the amp was idled with low enough bias and HV to show some slight color on the anode. The peak anode voltage at idle is about half the peak anode voltage under operation (a tube running at 3000 Vdc has about 6 kV dc on the anode peaks in normal class AB operation). If the tube came from the supplier with poor voltage breakdown but higher than the dc anode voltage, this idle break-in with anode color could help.

A good 3-500Z normally should hold off 10-14 thousand voltage of anode to grid voltage without internal arcing. If the tube was not pumped down and aged to fully getter, then you MIGHT just through luck get one that would not arc at 3000V (or some lower voltage), but would arc when RF was applied and peak voltage reached 5000 volts or so during full power RF operation. In this rare case, where breakdown was in the operating range but above the dc voltage, might benefit from aging with enough anode current to have a slightly red anode.

All of this really comes back to poorly manufactured tubes that have not been processed correctly at the factory. The odds of making a new bad tube good by "breaking it in" are very low, if not close to zero. The only real way to be effective is if the anode is heated to slight color to activate the getter. Filament alone won't do it for an internal anode power grid tube.

A tube with a metal/ceramic or metal/glass envelope can be aged with filament only, because they have the gettering material on the cathode structure. Running the filament getters external anode tubes. It does not getter internal anode power grid tubes.

Tom
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