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9 times outta 10 you won’t find a shorted tube ohming ?it with a meter.? If you catch a tube short with a meter it’s because the grid is obliterated and debris is all over.? Once Chinese tubes short best to Chuck in the garbage.

On Friday, September 8, 2023, 11:18 AM, Jim Strohm <jim.strohm@...> wrote:

Another piece of ham lore is -- if you run the heater for a day, the getter will get hot and absorb the gas.

That's worth a try, and won't set your backyard or basement on fire.

73

Jim N6OTQ

On Fri, Sep 8, 2023 at 10:07?AM Chuck Neal <cdoneal@...> wrote:

The tube is likely gassy and will only conduct when HV is applied.? It usually takes a few hundred volts for a gassy tube to conduct so the low voltage from a test meter will not reveal a gassy tube.

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Hint:? Watch the tube upon applying HV.? You might see a quick bluish flash before the fuse goes.

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-Chuck K1KW

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From: [email protected] [mailto:[email protected]] On Behalf Of Bob
Sent: Friday, September 08, 2023 10:21 AM
To: Ham Amplifiers Ham Amplifiers
Subject: [ham-amplifiers] 572B

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Hi all,

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I'll condense this, you'lll get the idea.

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A friend has an 811H with 3 year old 572B's. One shorted?and causes the fuse to blow immediately. Tube replaced and all is well.

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Measuring with a DVOM shows no shorts at all. I do know some tubes will short after they get warm/hot but this one blows the fuse immediately (no time to get hot) but does not measure any short circuit.

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I've now talked to two other hams on the air that say the exact same thing happened to them.

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What causes this??

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73, Bob? W4JFA