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Old 5th April 2004, 07:40 PM   #1
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Default Restoring tired tubes

I have tried successfully, a method of restoring the emission of tired old tubes

This involves setting up a variable PSU for the heater capable of around 20% more VOLTAGE, and a small (30v or so, more for high imp valves) bias between anode and cathode, All grids attached to anode, with a milliammeter in series with a resistor of suitable value to allow around 10% normal anode current to flow.

The method involves first setting up as above, and allowing the tube to stand for around half hour like this, passing around 10% current.

Then, increase the heater volts by 20%, and monitor the anode current, which will first rise quite quickly as the cathode heats up to the higher temp, and then will slowly climb to a maximum, and if left will start to fall again--The skill comes of when to judge the point of maximum current flow.

When this happens, decrease the heater back to normal value, and disconnect the Anode voltage source, but do not alter the anode series resistance, and leave for 1 hour, Check anode current again, There is often a great improvement. Leave for a further hour and check again, a smaller improvement is often noted, Keep checking every hour or so untill no further increase is noted, then the process is complete.

Its well worth trying out this process, especially as some of the valves we use are rediculously expensive!--Even if we only get say 50 more hours out of a valve, its worth it!

This wont of course cure a completely faulty or dead cathode, which may need even more heating to get things started Dont go over 20% CURRENT MAX, if you cant get any improvement at these extreme settings then the valve is finished!

Worth a try on that dead old WE 300B you have tucked away, but cant bear to bin!
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Old 5th April 2004, 08:43 PM   #2
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Hmmm sounds like an awful lot more hassle than the standard method of just heating it a bit extra. If current is required, it would seem to me a tube tester would be perfect. Even a cheap junker like my Eico 625, just hook up the tube as normal (per the roll chart), kick heater voltage up a tap, knock down the current selector a notch or two and hold down the test button for a few hours.

Tim
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Old 5th April 2004, 10:48 PM   #3
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Hi,

Quote:
knock down the current selector a notch or two and hold down the test button for a few hours.
ROTFLMAO....

Nah, for a 6.3V tube set Vf to 9V and let the cathode bake for 15 minutes.
If the tube has regained normal emission when reset to 6.3V Vf you had a lucky day...
If not, you're tube was going to die any day soon anyway.

Either way you will have shortened normal tubelife by about 10% as by the same process you will have vapourized barium ions aswell.

If it dies on you, you may have yourself some kitchensalt to spice up your supper when you decide to smash the tube in mere frustration...[joking].

There's a more complicated procedure for reviving tubes, even one to reprocess the entire thing...

Cheers,
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Old 6th April 2004, 12:53 AM   #4
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Of course, the only tubes rebuilt are industrial tubes, that is, 4CX10000 and up. I suppose if you had the glassblowing, re-getter-ing, vacuum-pumping and induction-heating equipment you could do it yourself to anything...but why bother rebuilding tubes when you can make your own with stuff like that...

Tim
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Old 6th April 2004, 01:08 AM   #5
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Hi,

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but why bother rebuilding tubes when you can make your own with stuff like that...
Reminds me of a discussion that was printed as it was recorded on tape by a Dutch team composed of a dealer/manufacturer and his crew, a Philips engineer, an editor and some other well respected engineers....

They discussed tubes, lifetime enhancement tricks, SQ pro quality tubes, reducing noise, repair...the works...

While discussing how to "repair" some flaky tubes the editor, in all seriousness, all of a sudden suggested reprocessing the tube with a magnetron oven....

Naturally, everyone bursted out in laughter.

Boy, I'll never forget that one....

BTW, Tim, is repairing those big transmitter tubes still done in the U.S?
I used to have some sources for those DUDs as they call them in the US, no idea whether they're still in business though...
With the advent of the Chinese lightbulbs they may have gone under...?

Cheers,
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Old 6th April 2004, 02:36 AM   #6
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No idea... Eimac is still around sorta but I only know they make bigass tubes...

http://www.cpii.com/eimac/index.html

Says Richardson Elec. knows where your duds need to go...

Tim
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Old 6th April 2004, 02:41 AM   #7
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Default Hmmm.......magnetron oven..........

QUOTE]reprocessing the tube with a magnetron oven....[/QUOTE]

Would a regular (home) microwave oven be of any use ?
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Old 6th April 2004, 02:46 AM   #8
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Hi,

Quote:
Says Richardson Elec. knows where your duds need to go...
Yeah....Never want to deal with them again but thanks anyway.

Ashok,

Quote:
Would a regular (home) microwave oven be of any use ?
That's what the poor man had in in mind.
Don't even think of putting a tube in it.

Cheers,
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Old 6th April 2004, 07:29 AM   #9
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You obviously didn't see a programme of British television called "Clarkson". For those not in the UK, we have an opinonated presenter (is there any other kind?) by the name of Jeremy Clarkson who is a sort of over-grown schoolboy who mostly reports on cars with big engines. However, he got his own chat show where he could be arrogant and overbearing for the entire programme (rather than having to share with other presenters). In it, he used to pull all manner of things in microwaves (usually with terminal results to both the contents and the microwave). He also found unconventional uses for hairspray.

I find him very entertaining, but it's un-PC to say so.
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Old 6th April 2004, 08:15 AM   #10
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Econco rebuilds transmitter tubes in the US.
Their rebuilt tubes operate as new and cost about half as much as a new tube.
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