Tube Cooling Sept 22, 2017 17:42:28 GMT 12
- Edited Jan 13, 2020 11:28:47 GMT 12 by Owen Y
Post by Owen Y on Sept 22, 2017 17:42:28 GMT 12
Back around WWII & after, studies conducted by vacuum tube manufacturers, commercial users & the military, have shown that tube life is inversely proportional to the temperature of the tube glass bulb envelope.  "Glass is a very poor thermal conductor and is virtually opaque to thermal radiation at temperature below 400deg C." This causes 'hotspots' on the tube glass envelope, adjacent to the tube plate.  (Info from PEARL white papers on their tube coolers.)
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Tube Cooling Sept 22, 2017 17:52:03 GMT 12
- Edited Sept 22, 2017 17:53:01 GMT 12 by Owen Y
Post by Owen Y on Sept 22, 2017 17:52:03 GMT 12
These are the PEARL brand 'tube coolers': (Matt black painted folded copper sheet.) www.pearl-hifi.com/03_Prod_Serv/Coolers/Coolers.htmlI use them for some tubes - not all of my tubes (because there is some 'damping' affect on the sound, with these wrapped around the glass bulb). Here is my linestage:  I would seriously consider coolers on costly power tubes.
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Pundit
Post by neilsan on Sept 22, 2017 20:34:37 GMT 12
Not enough room to fit them on my Radford STA/3.
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Post by Owen Y on Sept 22, 2017 23:18:13 GMT 12
Some amps have their tubes very tightly spaced, eg Audio Research. I had an STA25 once - you may find that PEARL coolers, because of their folded design, actually slide down nicely & 'dove-tail' together closely on those EL34s.. The metal TX cover probably adds some heatsinking.
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Post by Owen Y on Sept 22, 2017 23:43:35 GMT 12
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Post by colinf on Sept 30, 2017 6:29:57 GMT 12
I've been researching this very subject in the last few weeks. I remember how Audio Research used low speed fan cooling for the tightly spaced tubes in the D79 poweramp. I think my next big valve amp should have low speed fans in the baseplate to increase tube life. And to make a better heater for the room in winter.
AMR-iFi R&D
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