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 Post subject: Glowing 1U5
PostPosted: Jun Mon 21, 2021 10:38 pm 
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Joined: Mar Wed 31, 2021 10:42 pm
Posts: 3
I am working on another ZTO H500. I noticed that the 1U5 tube was glowi g. Changed tubes and that was glowing as well. There is a faint hum when the radio is on. Any idea's as to the cause?


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 Post subject: Re: Glowing 1U5
PostPosted: Jun Mon 21, 2021 11:43 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3033
Location: Cortez, Colorado
Is it a hum or maybe more like boooooooo?


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 Post subject: Re: Glowing 1U5
PostPosted: Jun Tue 22, 2021 12:11 am 
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Joined: Feb Tue 10, 2009 3:16 pm
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Location: zipcode 46235
Might check the dropping resistors on each tube on the filament chain. You shouldn't see a visible glow on any of those tubes unless in the dark.


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 Post subject: Re: Glowing 1U5
PostPosted: Jun Tue 22, 2021 2:48 am 
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Joined: Dec Thu 10, 2015 7:01 pm
Posts: 536
Location: Aurora, IL
Quote:
Might check the dropping resistors on each tube on the filament chain. You shouldn't see a visible glow on any of those tubes unless in the dark.
]

+1 ^

And you can test radio in battery mode if you have a connector and also use a DC bench supply for 9 volt source. Filament string should be drawing 50 ma with 9 volt A+ hooked up and radio turned on ( and AC cord plugged into chassis ). Don't have to hook up the 90 volt B+ source yet until after you verified A+ filament circuit is working okay. That's what I did on my T.O. when first checking out. Discovered my radio worked in battery mode but not AC mode due to open dropping resistor.


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 Post subject: Re: Glowing 1U5
PostPosted: Jun Tue 22, 2021 4:42 am 
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Joined: Feb Wed 04, 2015 12:26 am
Posts: 1634
make absolutely certain that the tube socket pins are clean, and I mean CLEAN and tight, check the condition of the wiring from point to point around the socket, desolder each wire, clean the solder tabs on the socket and resolder wires, making damn sure the connections are good and solid.

I ran into this situation on a Sherwood S1000II with 4 6BQ5/7199, one of the output tubes was flashing white. I was pulling my hair out, until I found a minute amount of corrosion on the pins.


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 Post subject: Re: Glowing 1U5
PostPosted: Jun Tue 22, 2021 1:36 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 10884
Location: Long Island NY
Glowing how? If you are seeing the filament in the center of the tube glowing then there is a problem in the filament circuit causing too much voltage to be applied. This needs to be fixed immediately or it will correct itself by burning out. As mentioned above, the filaments in most 1.4 volt battery tubes do glow but so faintly you can only see them in a darkened room.

A purplish glow around the other electrodes would suggest the tube has gone to air. Replacing it with one known to be good is the only recourse in that case.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


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 Post subject: Re: Glowing 1U5
PostPosted: Jun Tue 22, 2021 4:15 pm 
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Joined: Mar Wed 31, 2021 10:42 pm
Posts: 3
Thanks for the info, I will have to get out my tester and go to work.


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