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November 26, 2021, 04:03:58 PM

Author Topic: Extend life of 300B tube with a stress crack (Sophia Royal Princess)?  (Read 455 times)

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Offline aroide

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I thought this topic might belong here....

I have a BeePre with some Sophia Electric 300B Royal Princess tubes that I LOVE.  I found a strange crack all the way around 1 tube.  Its about 1/3" up from the base and has the 'getter' silver behind it.  I can barely feel the crack and the tube is still holding vacuum and working. It is way out of warranty, sadly.

I was looking for any ways to extend the life of this tube.  I have a windshield repair kit and UV lamp.  I thought that maybe putting a small bead of repair fluid around the tube and curing it with the UV lamp would seal the crack.  Or something like acrylic nail polish?  though the windshield repair fluid is a better match for the thermal expansion coefficient of glass.

Is there any hope?  If this fails, will it potentially take my speakers with it?  I love these tubes and would love to get a bit more time out of them.
Mac mini running Roon->
Mytek Brooklyn DAC+->
Darwin Truth RCA IC->
BeePre (BeeQuiet,  Mundorf Ag/Au/Oil, Sophia Royal Princess 300B)->
Audioquest Colorado->
Rogue Audio Atlas Magnum amp (Psvane small signal tubes, KT150s)->
Audioquest Gibraltar-speaker cables>
Magnepan 1.7 & REL T-5

Offline Paul Birkeland

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Re: Extend life of 300B tube with a stress crack (Sophia Royal Princess)?
« Reply #1 on: April 22, 2021, 05:15:02 PM »
I would just not even touch it and run it until the getter starts to turn white.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Paul Joppa

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Re: Extend life of 300B tube with a stress crack (Sophia Royal Princess)?
« Reply #2 on: April 22, 2021, 05:17:48 PM »
Thermal stresses seem the most likely risk, so don't go through too many on-off cycles - if you turn it on, don't shut down untill after the last listening of the day. That's all I can think of.

Mechanical shock seems another likely risk; don't tap it.
Paul Joppa

Offline aroide

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Re: Extend life of 300B tube with a stress crack (Sophia Royal Princess)?
« Reply #3 on: April 22, 2021, 05:53:47 PM »
Thanks for the quick responses.   I'll run it until its death.  Then I'll switch to my 'backup' Psvane Ti II tubes which are pretty good.  But those Royal Princess tubes have the most balanced, dynamic, and detailed sound of any I've tried.

Your preamp design is so good that the subtle difference in these tubes is clearly audible :-).
Mac mini running Roon->
Mytek Brooklyn DAC+->
Darwin Truth RCA IC->
BeePre (BeeQuiet,  Mundorf Ag/Au/Oil, Sophia Royal Princess 300B)->
Audioquest Colorado->
Rogue Audio Atlas Magnum amp (Psvane small signal tubes, KT150s)->
Audioquest Gibraltar-speaker cables>
Magnepan 1.7 & REL T-5