[Amps] NOS 8874 (3cx400)

[gudguyham at aol.com]

Those tubes getter with just filament voltage so to degas them run them with normal filament voltage and cooling.  Those tubes are very unlikely to get gassy but anything is possible so why not be safe and getter them for 24-48 hours.  Running lower plate voltage isn’t very helpful unless it’s a thoriated filament which it’s not so once you run it with filament voltage only for some time, that’s the best you could do.  Getting the anode hot doesn’t degas those tubes.  It’s very possible you can use them right off but no harm done waiting.  Being the tubes are rare and expensive being cautious is wise.  Good luck and HNY


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On Sunday, January 2, 2022, 4:22 AM, gd0tep at manx.net <gd0tep at manx.net> wrote:

Hi to the group,

I have been offered a  pair of new old stock 8874 tubes. These would be very nice to have for a rebuild project, BUT with  date codes in the 1980's, what would be the normal practice to get them back to normal expected output (I ask in the hope that this would be possible)

Should I run them up just on heaters & blower a few days, then try HV on them. Or slowly bring HV on over a period of time??

What's would be my best options??


Any advice would be much appreciated.


Thanks,

73
Andy
GD0TEP 

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