Heat transfer mechanisms
You forgot to mention conduction and this is certainly a large factor.
In the early days we did an oxide blackening process on the copper to get its emissivity up where it needed to be, i.e. in the .95 to .98, near black body, range. While that worked well enough there was always the matter of sketchy contact area in that the glass is never perfectly flat, the cooler doesn't perfectly conform to the glass, etc. Seeking to address this we used carbon fiber sleever for a couple of years but ran into supply issues as we weren't buying 100s of pounds at a time.
The last couple of years I've worked at powder coating the parts and that is a good solid solution with a number of benefits:
- having a high metal content the coating is very thermally conductive
- being essentially a plastic, the coating softens slightly with heat; and with time and pressure it slightly flows to accurately conform to the bulb's shape thereby greatly enhancing the otherwise minimal areas of direct contact and enhancing thermal conduction
- with earlier coolers some users claimed to hear a slightly 'egdy' sound imparted by their use. While we never did hear this, I listened to the users' feedback and came to the notion that there could well a mechanism where 'micro rattles,' cooler against glass, might be occurring. The powder coat kills that possibility
- lastly, removing a cooler from a cold tube one finds it slightly stuck to the glass, and over a substantial area yet the cooler breaks loose with no problems at all. The point here is that, again, being a plastic, the coating can be reasonably expected to have worthwhile damping effects in respect of anything that might be going on in the glass.
Not having done lab work to investigate glass vibration, I think it a tertiary effect at best and one rather overblown by those making 'tube dampers' of various sorts, the powder coat/copper against the glass can be reasonably expected to damp whatever might be happening.
Maybe one day I'll dream up a way to look at that with scanning laser vibrometry . . . something we can do around here ;-)
You forgot to mention conduction and this is certainly a large factor.
In the early days we did an oxide blackening process on the copper to get its emissivity up where it needed to be, i.e. in the .95 to .98, near black body, range. While that worked well enough there was always the matter of sketchy contact area in that the glass is never perfectly flat, the cooler doesn't perfectly conform to the glass, etc. Seeking to address this we used carbon fiber sleever for a couple of years but ran into supply issues as we weren't buying 100s of pounds at a time.
The last couple of years I've worked at powder coating the parts and that is a good solid solution with a number of benefits:
- having a high metal content the coating is very thermally conductive
- being essentially a plastic, the coating softens slightly with heat; and with time and pressure it slightly flows to accurately conform to the bulb's shape thereby greatly enhancing the otherwise minimal areas of direct contact and enhancing thermal conduction
- with earlier coolers some users claimed to hear a slightly 'egdy' sound imparted by their use. While we never did hear this, I listened to the users' feedback and came to the notion that there could well a mechanism where 'micro rattles,' cooler against glass, might be occurring. The powder coat kills that possibility
- lastly, removing a cooler from a cold tube one finds it slightly stuck to the glass, and over a substantial area yet the cooler breaks loose with no problems at all. The point here is that, again, being a plastic, the coating can be reasonably expected to have worthwhile damping effects in respect of anything that might be going on in the glass.
Not having done lab work to investigate glass vibration, I think it a tertiary effect at best and one rather overblown by those making 'tube dampers' of various sorts, the powder coat/copper against the glass can be reasonably expected to damp whatever might be happening.
Maybe one day I'll dream up a way to look at that with scanning laser vibrometry . . . something we can do around here ;-)
Only if correct, which it is not . . .
This is correct but conduction is a large factor
If it is not, conduction is not a large factor.
If it is not, heatsinks would not work.
While I haven't studied the matter enough to be sure that what you suggest is incorrect, it might well be the case, and I've spoken at length with FLIR about the matter.
They tell me that IR CCDs (I assume) can made responsive to various wavelengths i.e. temperatures, and that I can get snaps of the glass while remaining 'blind' to the higher temp parts within it.
We'll see . . . and at $300.0/day to climb that learning curve I'm doin' my d*mned homework first ! !
Still, that is far too hot and parts run that way will die much sooner than if run cooler. I have a customer who has run his cooled KT90s several hours a day, every day, for seventeen straight years . . . That's longevity old son.
Thanks for all that, this thread is getting to be some real fun . . .
Are we to understand that it is only tube coolers made in the last couple of years, with the powder coating, which actually work correctly by using conduction to equalise glass temperature?
Earlier ones had uneven glass contact so could sometimes magnify temperature variations? Earlier ones absorbed radiated heat which was already outside the glass, and then re-radiated some of it back in again? If so, I can understand why it took 81 posts before this information was volunteered.
Earlier ones had uneven glass contact so could sometimes magnify temperature variations? Earlier ones absorbed radiated heat which was already outside the glass, and then re-radiated some of it back in again? If so, I can understand why it took 81 posts before this information was volunteered.
Everything re-radiates back. When you enter the cold house and switch on an air heater, do you feel how cold are walls? When you enter a hot house and switch on air conditioner, do you feel radiation from walls?
Heatsinks can't radiate back to anodes more than they absorb. But they can have large enough surface area to be cooled down by convection. Also, being black outside they radiate from much bigger surface than anodes have. You can't absorb heat from anodes by convection, but you can organize forced air flow near heatsinks.
"Still, that is far too hot and parts run that way will die much sooner than if run cooler. I have a customer who has run his cooled KT90s several hours a day, every day, for seventeen straight years . . ."
Well, I do cool my tube amps with air flow from a quiet fan in the chassis and recessed sockets. I could see maybe adding a small/short tubular air guide above deck to keep the air closer to the tube surface. But my tubes only cost around $1, a $19 tube cooler could buy me a whole box of tubes, for the next century.
Well, I do cool my tube amps with air flow from a quiet fan in the chassis and recessed sockets. I could see maybe adding a small/short tubular air guide above deck to keep the air closer to the tube surface. But my tubes only cost around $1, a $19 tube cooler could buy me a whole box of tubes, for the next century.
Here is a picture of my last amp prototype that uses tubes in normal regimes, attached. Perforated aluminium chassis allows free air convection, and spreads heat well due to thermal conductance of aluminium. Capacitors are below, so cooled by the coldest in the amp air. Mirrors reflect rays preventing heating of transformers by tubes.
But in this particular topic I was asking about source of coolers because I want to run 6С19П tubes with higher anode dissipation power than allowed by manufacturer...
But in this particular topic I was asking about source of coolers because I want to run 6С19П tubes with higher anode dissipation power than allowed by manufacturer...
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Yes, everything radiates back. However, something immediately outside the glass will send almost all its radiation back into the glass. Something further away could be cooler, so radiates less, and much of its radiation will miss the valve and hit other objects instead.
As a general rule, you don't cool something by covering it with something else, as this blocks both radiation and convection. We normally insulate things by covering them. The exception is conduction cooling but for this to work you need high thermal conductivity at the interface, which it seems the tube coolers only recently obtained.
As a general rule, you don't cool something by covering it with something else, as this blocks both radiation and convection. We normally insulate things by covering them. The exception is conduction cooling but for this to work you need high thermal conductivity at the interface, which it seems the tube coolers only recently obtained.
No, the earlier parts also used conduction, obviously, they contacted the glass didn't they . . .
I didn't say that conduction was the only heat transfer mechanism, I said it was one of the three commonly considered and we'd enhanced that aspect. I did not say, nor did I imply that the product was inadequate. I said we had improved it
The relevant matters here have to do with product development and the willingness to do it in the first place.
I'm unsure as to your reasoning here, how could uneven contact bring a about an increased temperature; something I never saw in any of the hundreds of measurements I did over the years ? ?
It is called Mirror
I remember a laboratory work we did in TIASUR, when professor gave some cans with glossy enamel spray of different colors; asked to rate and write down own expectations, then did actual measurements. "General Rule" - driven students were very surprised.
The matter is in coefficient of blackness.
Glass and charcoal of the same temperature look differently on the screen.
Good idea! In Siberia we had wooden curtains (kind of doors, called Ставни) outside of glass windows. We used them during winter nights.
So the earlier coolers had minimal contact, so presumably poor thermal conductivity at the interface? Points of contact would be cooled, everywhere else would have a thin layer of air so hotter?
I didn't say increased temperature, I said increased temperature variation.
I said that conduction cooling was the exception.
A black surface (the best option) immediately outside the glass could radiate up to half its thermal loss back into the valve. The rest, plus any convection, would go the other way. A surface further away could radiate much less back into the valve.
My point is that radiation and convection are likely to be worse with a cooler than without. A cooler can only improve things by using conduction, which requires good contact all over the glass. It seems that this has only recently been achieved.