KT88 mounting question

PWR RYD · 12th December 2011, 07:04 PM

This might be a really silly newbie question, but here goes: I was reading page 5 of the Genalex KT88 data sheet. It states:

"Installation

The tube may be mounted either vertically or horizontally.
When tubes are mounted vertically it is recommented that the centres of the
tube sockets are not less than 4in. apart and that pins 4 and 8 of each tube are in line."

I understand the minimum spacing for adequate ventilation, but why do the tubes need to be "clocked" a certain way when they are standing up (i.e. not mounted horizontally)?

Thanks for any insight.

HollowState · 12th December 2011, 07:27 PM

Quote:

Originally Posted by PWR RYD

but why do the tubes need to be "clocked" a certain way when they are standing up (i.e. not mounted horizontally)?.

I've never read this directive before, but I'll take a good guess at it. Orienting the tubes a particular way is probably to prevent the "hot" side of the plates from facing each other. The hot side would be the side that sees the wide face of the cathode. If the tubes are spaced more then the minimum of 4 inches apart, then it probably doesn't matter.

ChrisA · 12th December 2011, 09:42 PM

Quote:

Originally Posted by PWR RYD

...
I understand the minimum spacing for adequate ventilation, but why do the tubes need to be "clocked" a certain way when they are standing up...

Tubes cool by radiation. After all, the plates are in vacuum so there is no other way. I think they are saying not to have the hot parts of the plates facing each other.

astouffer · 12th December 2011, 10:02 PM

Probably to stop things from sagging internally when they heat and expand.

HollowState · 12th December 2011, 10:14 PM

Quote:

Originally Posted by astouffer

Probably to stop things from sagging internally when they heat and expand.

Nope, that would be true if they were mounted horizontally, but we're talking vertical in the original question.

costis_n · 13th December 2011, 06:12 AM

It is because they are beam power tubes, so they are not symmetrical. The "clocking" is specified so that the beams (which make the anode, hence the envelope hotter) are not facing each other, i.e. so that the tubes are not heating each other.

PWR RYD · 13th December 2011, 12:31 PM

Makes perfect sense. Thanks.

12th December 2011, 07:04 PM	#1
PWR RYD diyAudio Member Join Date: Nov 2009 Location: Rockford, IL	KT88 mounting question This might be a really silly newbie question, but here goes: I was reading page 5 of the Genalex KT88 data sheet. It states: "Installation The tube may be mounted either vertically or horizontally. When tubes are mounted vertically it is recommented that the centres of the tube sockets are not less than 4in. apart and that pins 4 and 8 of each tube are in line." I understand the minimum spacing for adequate ventilation, but why do the tubes need to be "clocked" a certain way when they are standing up (i.e. not mounted horizontally)? Thanks for any insight.

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12th December 2011, 10:02 PM	#4
astouffer diyAudio Member Join Date: Jun 2004 Location: Pittsburgh, crumbling wasteland	Probably to stop things from sagging internally when they heat and expand.

13th December 2011, 06:12 AM	#6
costis_n diyAudio Member Join Date: Aug 2008	It is because they are beam power tubes, so they are not symmetrical. The "clocking" is specified so that the beams (which make the anode, hence the envelope hotter) are not facing each other, i.e. so that the tubes are not heating each other.

13th December 2011, 12:31 PM	#7
PWR RYD diyAudio Member Join Date: Nov 2009 Location: Rockford, IL	Makes perfect sense. Thanks.