Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Heatsinks for tubes?
Heatsinks for tubes?
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 5th December 2011, 09:29 PM   #221
SemperFi is offline SemperFi  Wake Island
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
Quote:
Originally Posted by Wavebourn View Post
The thread was started a year ago, of course you did not have a time to read it, especially that part where I wrote that I gave up the idea because naked lamps look prettier.

The funny thing is I got this 'deja vu' feeling thinking 'havent I seen this thread before?' I wouldnt be surprised if I've posted in it when it was fresh. Perhaps I'll read it tonite in it's entirety.
  Reply With Quote
Old 19th January 2012, 07:57 PM   #222
DIM is offline DIM  Russian Federation
diyAudio Member
 
DIM's Avatar
 
Join Date: Sep 2005
Location: St. Petersburg, Russia
Does anybody tell me, where I can find big heat sink for 3cx300a1 (gm-5b) or complete cooling system?
  Reply With Quote
Old 19th January 2012, 08:16 PM   #223
Mother of PEARL is offline Mother of PEARL  Canada
diyAudio Member
 
Join Date: Mar 2010
Location: Calgary, Ab, Canada
While I did at one time make such a heatsink, data on which you can download from here http://www.pearl-hifi.com/06_Lit_Arc...Data_Sheet.pdf I no longer make the part and I know of no other source
__________________
Bill Perkins @ PEARL
Commercial Site: www.pearl-hifi.com
  Reply With Quote
Old 19th January 2012, 08:30 PM   #224
DIM is offline DIM  Russian Federation
diyAudio Member
 
DIM's Avatar
 
Join Date: Sep 2005
Location: St. Petersburg, Russia
No one no where? Understood. Will try use Eimacs socket - chimneys...(

Bill, can You make for me some heat sinks?

Regards, Dmitry.
  Reply With Quote
Old 24th May 2017, 12:10 AM   #225
sser2 is offline sser2  United States
diyAudio Member
 
Join Date: Jan 2003
Location: Pittsburgh, PA
I came across this thread and read it with much interest. Since the thread ended up kind of inconclusive, I looked for more information trying to answer the following questions:

Q1. How infrared radiation from hot plate depends on plate temperature, environment temperature, and other factors?

Q2. How much infrared radiation from hot plate passes through the glass, is absorbed by the glass, and transmitted back off the glass to the plate?

Q3. What factors contribute to heat dissipation from glass envelope and how envelope cooling can be improved?

A1. Power radiated by plate is governed by Stefan-Boltzmann equation:

P=KεA(Ta^4 – Te^4), where

K, Stefan-Boltzmann radiation constant;
ε, emissivity factor, values ranging from 0 to 1, the latter being emissivity of absolute black body;
A, radiating area of plate;
Ta, plate temperature in degrees of Kelvin;
Te, glass envelope temperature in degrees of Kelvin.

The factor having most influence on heat radiation is plate temperature, because heat transfer by radiation is proportionate to fourth power of absolute temperature. Glass temperature has lesser, but not negligible effect. At typical plate temperature of 400C and glass temperature of 200C, about 25% of energy is radiated by glass back to plate. If glass temperature is reduced to 100C, the energy radiated back to plate will be only about 10%. Accordingly, for a tube having 25W plate dissipation rating, keeping glass at 100C will allow safely increasing plate dissipation to 28.75W. This answers OP's question about whether tube cooling allows increasing plate dissipation. It does.

ε has profound effect on energy radiation. Shiny metal surface has ε of about 0.1, grey alumina-blasted metal is 0.3-0.4, black polished metal is 0.6-0.7, and black carbonized metal with matte surface may be as high as 0.98. Thus, examining plate appearance may tell something about power rating. It is not surprising why a 807 tube with black carbonized plate is rated 25W, but similar 6BG6G with shiny black plate is only 20W.

"A" seems straightforward - larger plate area will radiate more power. However, plate surface temperature may be not uniform, depending on tube construction. Iron or nickel plate alloys have relatively poor heat conductance (Ni is 2 times more conductive than Fe), which is exacerbated by low thickness of material (ca. 0.1-0.2mm). Beam power tubes have very uneven heat distribution across the plate, whereas true power pentodes are much more even in this respect, thus allowing more efficient use of radiating surface.

A2. At the typical working plate temperature of 400C, the wavelength of IR radiation is broadly distributed from 1.5 to over 10 microns, with peak at 4 microns. Soft glass typical of most tubes has transmissivity of about 0.55 at 4 microns, and virtually zero at 5 microns and above. About 35% of total 400C IR passes through soft glass. Roughly 5% is reflected back to plate (this is in addition to Stefan-Boltzmann heat transfer), and the remainder 60% is absorbed by the glass. It might be counterintuitive, but glass has ε of 0.92-0.94 for IR, so it radiates and absorbs heat quite efficiently despite its smooth surface.

Although glass is poor heat conductor (1/30 conductivity of steel), temperature gradient across 1 mm glass thickness does not exceed 2-3C under rated power conditions. However, temperature gradients along the glass envelope may be as high as 150C. This is not a practical concern though, as long as rated temperature at the hottest point is not exceeded.

A3. As discussed, 35% of plate's heat passes through, and the rest is absorbed by the glass. Of the absorbed portion, some is radiated into environment according to Stefan-Boltzmann law, and the remainder is dissipated by air convection. For a tube with 100 cm^2 surface area with average envelope temperature of 130C and environment of 30C (DIY amplifier without enclosure), the calculated power radiated from envelope is about 1W, and dissipated by convection is 15W. So, convection dominates heat dissipation by envelope. Under equal conditions, large envelope is more effective at dissipating heat than smaller envelope for both radiation and convection, with heat transfer proportionate to square of envelope's diameter.

A tube cooler like Pearl's changes the balance of tube cooling by virtually eliminating heat radiation into environment (40% of total) and substituting it for convection. To be effective, the cooler must have surface area much larger than envelope's, and made of highly conductive material. Heat transfer at the glass-cooler interface may be a problem. Because heat radiation plays minuscule role in cooler's function, black painting is not necessary, but providing for good air convection is. However, good air convection around naked tube may be sufficient for keeping glass at safe temperature without sacrificing the benefits of radiation cooling.

Sorry for being too long.
  Reply With Quote
Old 24th May 2017, 12:22 AM   #226
sser2 is offline sser2  United States
diyAudio Member
 
Join Date: Jan 2003
Location: Pittsburgh, PA
A side note. Proper function of sacrificial getters requires certain high temperature. In many power tubes, getters are located vis-a-vis plate's hot spot. In such tubes, external cooler may interfere with getter function.
  Reply With Quote
Old 24th May 2017, 02:17 AM   #227
popilin is offline popilin  Argentina
diyAudio Member
 
popilin's Avatar
 
Join Date: Oct 2010
Location: Traslasierra
Quote:
Originally Posted by sser2 View Post
A1. Power radiated by plate is governed by Stefan-Boltzmann equation:

P=KεA(Ta^4 – Te^4), where

K, Stefan-Boltzmann radiation constant;
ε, emissivity factor, values ranging from 0 to 1, the latter being emissivity of absolute black body;
A, radiating area of plate;
Ta, plate temperature in degrees of Kelvin;
Te, glass envelope temperature in degrees of Kelvin.
That is not the Stefan-Boltzmann equation, Stefan–Boltzmann equation states that the total energy radiated per unit surface area of a black body across all wavelengths per unit time is

E = σ T

Where σ = 5.67 x 10⁻⁸ W/(m² ºK) is the Stefan-Boltzmann constant, and T is the absolute temperature of the emitter surface.

For a black body of area A, radiated power across all wavelengths is

P = A σ T

For other than ideal black bodies

P = ε A σ T

Where ε is the emissivity, ε<1

If the body, at temperature T is radiating energy to its cooler surroundings at temperature Tc, then

P = ε A σ (T⁴ - Tc⁴)

Note that emissivity is also function of the temperature

ε = ε (T)

So we must cheat to derive that you stated as Stefan-Boltzmann equation.
__________________
I do not suffer from insanity, I enjoy every minute of it. - Edgar Allan Poe
He has the most who is most content with the least. - Diogenes of Sinope

Last edited by popilin; 24th May 2017 at 02:21 AM.
  Reply With Quote
Old 24th May 2017, 03:26 AM   #228
popilin is offline popilin  Argentina
diyAudio Member
 
popilin's Avatar
 
Join Date: Oct 2010
Location: Traslasierra
Quote:
Originally Posted by sser2 View Post
A tube cooler like Pearl's changes the balance of tube cooling by virtually eliminating heat radiation into environment (40% of total) and substituting it for convection.
<snip>
Because heat radiation plays minuscule role in cooler's function, black painting is not necessary, but providing for good air convection is.
In the usual case that environment temperature Te is smaller than cooler temperature Tc, your statement is wrong because the cooler still radiates as

P = ε A σ (Tc⁴ - Te⁴)

And black painting is intended to make the cooler as "black" as possible, increasing
ε, remind you that a black body is the best emitter and at the same time the best absorber, that is also the reason of carbonized anodes.

__________________
I do not suffer from insanity, I enjoy every minute of it. - Edgar Allan Poe
He has the most who is most content with the least. - Diogenes of Sinope

Last edited by popilin; 24th May 2017 at 03:43 AM. Reason: Adjust letter size
  Reply With Quote
Old 24th May 2017, 06:28 AM   #229
sser2 is offline sser2  United States
diyAudio Member
 
Join Date: Jan 2003
Location: Pittsburgh, PA
Quote:
Originally Posted by popilin View Post
That is not the Stefan-Boltzmann equation, Stefan–Boltzmann equation states that the total energy radiated per unit surface area of a black body across all wavelengths per unit time is

E = σ T...

So we must cheat to derive that you stated as Stefan-Boltzmann equation.
Yours is the simplified equation for the case of absolute black body radiating into infinite space. My formula is for radiation energy exchange between two bodies with different temperatures. The Te component can be ignored with large temperature difference, but not when the difference is not so large.
  Reply With Quote
Old 24th May 2017, 06:29 AM   #230
trobbins is offline trobbins  Australia
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
sser2, you would need to provide some mathematical support for a few of the values you use, especially relating to power transfer through glass, as that is an integration across a frequency span, where the transmittance varies with frequency, and the power density is a function of frequency and source temperature.

There is also an issue with your description of radiation power flow - transfer is from hotter to colder surfaces, not the other way.

The glass thickness has a significant effect on transmission profile with frequency, as indicated in that app note AN109.
  Reply With Quote

Reply


Heatsinks for tubes?Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
FS: 2 Tung-sol 45 tubes, 2 Westinghouse 5u4gb tubes athos56 Swap Meet 0 3rd August 2010 11:18 PM
Intel CPU heatsinks as power output transistor heatsinks? deltavektor Solid State 4 29th November 2009 01:47 PM
FS Heatsinks, tubes, drivers and amps. eapavant Swap Meet 9 29th April 2008 01:00 AM
CV428 tubes (Loktal 807) tubes FS mobyd Swap Meet 3 2nd January 2008 11:26 AM
Caps, xformers, rectifiers, heatsinks, Zen PCBs, tubes and jacks krikor111 Swap Meet 13 15th February 2005 02:42 AM


New To Site? Need Help?

All times are GMT. The time now is 11:03 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki