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Old 07-17-2018, 10:43 PM
Sealtest Sealtest is offline
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Join Date: Dec 2017
Location: Knoxville, Tennessee
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How bright should a rectifier tube get??

I was putting a tv on a variac and noticed the flyback wasn't kicking in. I looked inside the set and saw that the rectifier tube was brighter than any tube I have ever seen. Was this maybe okay and I have just never seen a tube that got this bright? I shut the tv down around 100vac but I am not certain.

This is a 1955 RCA victor tv.
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Old 07-18-2018, 02:02 AM
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Electronic M Electronic M is offline
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Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
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Bright heater unusual, but not necessarily bad. If the plate of the tube was glowing that is BAD very bad...Redplating occurs when a tube is passing far more plate current then it is designed to handle. This occurs in rectifiers when there is excessive load, and in triodes/tetrodes/pentodes when there is either too much load or more often when the grid bias is wrong. Redplating usually destroys tubes in seconds to minutes, and should not be allowed to occur for an extended period of time unless you enjoy paying for replacement tubes.

A redplating rectifier is probably a symptom of a B+ short, shorted lytic, or some stage HEAVILY loading the B+. If you have it you need to fix it first before anything else. A DMM/VTVM/VOM is your best friend if the source of the fault is not obvious.
Tom C.

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Reading between the scan lines since the mid 2000's.
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Old 07-18-2018, 04:03 AM
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Celt Celt is offline
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Some good advice there...

Let me live in the house beside the road and be a friend to man.
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Old 07-18-2018, 07:16 AM
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init4fun init4fun is offline
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Yes indeed , if this is the "LV rectifier" (5U4 usually) the filaments should be a dull cherry red , to possibly a light washed out orange , and no brighter . If the plates show any color at all other than black , like how the poor 5Y3 in my avatar has it's plates glowing orange , there is a short in the B+ line and just like Tom (E.M.) said the tube and or power transformer will be destroyed if such operation is allowed to continue much beyond a few seconds or so ...
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