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[compasspnt]

This may be a naive question, and is completely distinct from the question of potential sound quality, but would there not be "extra" heat buildup by having the glass tube inside of the metal can?

[J.J. Blair]

That is a good question, Terry.  

On an unrelated note: I did notice that the U47 with the VF14k tube costs $1,500 more than one with an EF14.  

[kats]

Yes and it includes a "historic" PSU and the suitcase. Similar to the Ela M251 E vs F models.

[David Bock]

Quote:

This may be a naive question, and is completely distinct from the question of potential sound quality, but would there not be "extra" heat buildup by having the glass tube inside of the metal can?

Even with undervoltage filament heating you would find this to be true. Additionally, you reduce the life of the tube. There are old studies illustrating this, even to the point of what part of the tube gets how hot and where to heat sink them.

[Barry Hufker]

Heat dissipation: Why not use some sort of heat-transferring gel and let the metal casing be the heatsink?

[rodabod]

Might be tricky to assemble, depending on how the cap fits as the heat-transferring substance would have to have very good insulation properties and probably not touch the base.

Might be an idea if they made the can metal and made a mount inside for the valve.

[Rick O'neil]

anybody ever pulled a  real vf14m apart..?
did you find a  seperate glass tube inside ..?
isnt the metal case a shielding thing .?

i did trash a noisy (doh !) tube about 15  years ago  but didnt have the sense to photograph it  or keep the tube for that matter  but i am  kinda sure i saw that  it was glass tube inside the vf14m

so anyone got a photo of an old  real one in pieces to share to us  ?

[kats]

dbock wrote on Wed, 18 February 2009 16:52

Even with undervoltage filament heating you would find this to be true. Additionally, you reduce the life of the tube. There are old studies illustrating this, even to the point of what part of the tube gets how hot and where to heat sink them.

Really, you mean they actually have studies that describe the dissipation of heat between a glass tube, a steel tube, and then how it compares to a glass tube within a steel tube? I find that remarkable.

Or were you just trying to point that heat affects the life of a tube and that there are studies to corroborate? If so, I would like to thank you for the revelation and putting into a context that would completely leave a wrong impression to the original question.

[ToddP]

Why is that remarkable? They were using glass and metal tubes in every type of electronic equipment for decades. I would find it remarkable is they DIDN'T study it.

[David Bock]

Yup. Military research.

[J.J. Blair]

Rick O'neil wrote on Wed, 18 February 2009 23:27

anybody ever pulled a  real vf14m apart?...I am  kinda sure I saw that it was glass tube inside the VF14M So anyone got a photo of an old  real one in pieces to share to us  ?

I don't see the glass, or even room for it.  This is VF14 and a UF14.

(I took the picture of the two tubes, after sawing the metal domes off. These pictures where posted  on this forum about a year ago. There is no glass, and no need for it: the tube's vacuum is formed with just the metal caps hard soldered to the metal bottom plate (visible as a silver colored plate in the picture) which is glued to the plastic bottom plate that contains the holes for the eight pins. K.H.)

[kats]

The question was how does glass INSIDE a metal tube affect heat dissipation, not the different dissipation properties of metal & glass.  

[ToddP]

I know. And there were tubes made that did that. Put glass tubes in a metal shielding.

[Rick O'neil]

Great seeing those VF/UF14 insides; thanks!
Quite different from the opening post's picture

I really cannot remember what was in the VF14-type tube I trashed, but I have a dim memory of opening a metal tube of some kind and finding a glass tube inside- maybe a 6V6 or a C3 hifi tube ? - I dunno.

I guess the point was I was sure some "metal tubes" were glass tubes inside a metal can and the can just acted as a shield, so  those kind of heat studies Mr Bock was referring to seemed logical to me.  

[compasspnt]

Rick O'neil wrote on Thu, 19 February 2009 15:20

I really cannot remember what was in the VF14-type tube I trashed, but I have a dim memory of opening a metal tube of some kind and finding a glass tube inside- maybe a 6V6 or a C3 hifi tube ?

Then, as you now can see, the tube was not an authentic VF14M.