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Author Topic: 3-500Z Tube Failure  (Read 1125 times)
W0XX
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Posts: 1437




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« on: December 04, 2017, 07:56:33 AM »

What are the typical symptoms if a 3-500Z open or shorts in an amp?

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K8AXW
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« Reply #1 on: December 04, 2017, 09:34:04 AM »

Many answers...from no current draw on keydown to catastrophic destruction of one or more components.

Do you have specific symptoms or just a general question?
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K3VW
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« Reply #2 on: December 04, 2017, 09:39:34 AM »

One thing that occurs is if it showing negative grid current on key down, it has a grid-to-filament short, it can be fixed about 50% of the time by putting 120VAC between the grid and filament. Be carefull ! Check the tube with an ohmmeter. If it doesn't light up at all, check below filament pins on the chassis for melted solder.
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W0XX
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« Reply #3 on: December 04, 2017, 10:01:25 AM »

Not keying it yet.  Tube does not light up in the socket.  Another tube swapped in does.  Replacing the suspect tube does not light up.  I did not upon really looking into the tube, a very small piece of what looks like a staple wire sliding around.  Likely a piece of filament, likely shaken loose during transit.  I am guessing the tube is "open".
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K8AXW
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« Reply #4 on: December 04, 2017, 09:31:19 PM »

Looks like you have a bad tube OM..... Open filament.  Check the continuity between the filament pins with an ohmmeter.
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K4JJL
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« Reply #5 on: December 05, 2017, 07:07:00 AM »

I have had plate to grid shorts which blows up all kinds of components.  It's usually cause by someone running the amp laying on its side causing the grid to sag into the plate.
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WA2ISE
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« Reply #6 on: December 05, 2017, 01:11:06 PM »

caused by someone running the amp laying on its side causing the grid to sag into the plate.

Look at any tube datasheet, and there's always a spec on operating position.  Some tubes will work with "any" and others describe allowed positions.  To avoid sagging filaments or grids shorting to something. 

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W0XX
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« Reply #7 on: December 05, 2017, 04:54:32 PM »

I have never been a fan of horizontally mounted tubes...
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KM1H
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Posts: 2666




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« Reply #8 on: December 09, 2017, 05:28:56 PM »

Ive worked on 1-3 tube 3-500 amps for decades and a short time on their side hasnt hurt anything but I wouldnt do a long key down test either.
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AA2UK
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Posts: 381




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« Reply #9 on: December 10, 2017, 01:31:19 AM »

Not keying it yet.  Tube does not light up in the socket.  Another tube swapped in does.  Replacing the suspect tube does not light up.  I did not upon really looking into the tube, a very small piece of what looks like a staple wire sliding around.  Likely a piece of filament, likely shaken loose during transit.  I am guessing the tube is "open".
Since you have nothing to lose try re-soldering the filament pins on the 3-500Z.
I've brought a few back from the grave doing this.
This assumes the filament voltage is there and the seals are intact in the tube.
Bill, AA2UK
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AF6AU
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Posts: 64




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« Reply #10 on: Yesterday at 09:10:39 AM »

Being an owner of a Henry amp that uses 3-500's and 3-400's, if you have bits floating around inside the tube's vacuum volume, it's done for. You risk doing damage to the amp just "testing" it.

Considering the costs of new bottles verses new bottles AND repairs, why risk it at all?
Start saving the $$$ my firend, I know what you are buying soon.

2 questions,
1: What type of 3-500 was it? Metal plate, graphite plate?
2: Ballpark, how many filament "ON" hours did you get from it?

That would be good info for all of us.

FYI when I obtained the henry, it had 1990's Eimacs in it (end era of Eimac 3-500 with bad plate/glass seals), and it sat for 20 years. They were so gassy they glowed pink in my getter rig with only 200 plate volts. Sigh  Cry ... However I also have late 1960's 3-400's that work perfect  Smiley
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KM1H
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« Reply #11 on: Today at 02:05:58 PM »

Quote
FYI when I obtained the henry, it had 1990's Eimacs in it (end era of Eimac 3-500 with bad plate/glass seals), and it sat for 20 years. They were so gassy they glowed pink in my getter rig with only 200 plate volts. Sigh  Cry ... However I also have late 1960's 3-400's that work perfect  Smiley

I have a pair of very early Eimac's with the graphite anodes as built by Philips as Eimac was having production issues with theirs. These came from a SB-220 being converted to 6M around 1998 and the owner wanted new tubes. Ive put  RF thru them every couple of years and no funny glow yet.

I cant remember ever seeing a gassy 3-400Z or 3-1000Z but plenty NOS 4-400A and 4-1000A.
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