forced aircooling - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

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

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 February 2009, 12:04 AM   #1
diyAudio Member
 
Join Date: Jan 2009
Default forced aircooling

hi there

a thought that's been on my mind for some time. how much would you be able to push a tube with some serious aircooling? say, a 300B with some massive noisy fans (i can put my amps in another room, or even outside), would you be able to push it to 50-60W? more?

i know it's common with big **** transmitter tubes etc ..

cheers,

mb4b
  Reply With Quote
Old 5th February 2009, 12:18 AM   #2
nhuwar is offline nhuwar  United States
diyAudio Member
 
nhuwar's Avatar
 
Join Date: Jan 2007
Location: Cypress Texas
You could try and push it a little but not to much, maybe a few extra watts.

Nick
  Reply With Quote
Old 5th February 2009, 12:21 AM   #3
diyAudio Member
 
Richard Ellis's Avatar
 
Join Date: Sep 2006
Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.
No not really .JJs' 'hot' 300B is rated at 40 watts.
You are assuming there is a direct connection between heat generated and power, there really is none. Seen the insides of a tube? Lotsa fine delicate stuff inside, easy to make fireworks with.
______________________________________-Rick...........
  Reply With Quote
Old 5th February 2009, 12:41 AM   #4
nhuwar is offline nhuwar  United States
diyAudio Member
 
nhuwar's Avatar
 
Join Date: Jan 2007
Location: Cypress Texas
I agree will Richard. It's been common practice for ham operator to push tubes but it's always a gamble. And that is with old quality made tubes, most new stuff I doubt could handles this. But when it all comes down to it, it's your call, just remember most fac glass tubes have a chimney and ducting for the air to be routed around the pins.


As you push a tube harder past it's rating you will start to lose the vacuum.

Nick
  Reply With Quote
Old 5th February 2009, 12:45 AM   #5
m6tt is offline m6tt  United States
diyAudio Member
 
Join Date: Aug 2007
Air cooling in glass envelope tubes only allows the envelope temperature to be kept low. The plate radiates heat, and so it doesn't matter what you blow at it, it's in a vacuum. That being said, it might allow you to push it in tubes where the bulb will fail before the plate starts outgassing bad. The transmitter tubes that are forced air cooled have *external anodes*, which means some of the plate structure is out "here" in plain air. This allows the direct cooling of the plate with convective means, but also means you have a big piece of high conductivity metal with a couple thousand volts on it hanging out nearby.
  Reply With Quote
Old 5th February 2009, 12:59 AM   #6
nhuwar is offline nhuwar  United States
diyAudio Member
 
nhuwar's Avatar
 
Join Date: Jan 2007
Location: Cypress Texas
Quote:
Originally posted by m6tt
Air cooling in glass envelope tubes only allows the envelope temperature to be kept low. The plate radiates heat, and so it doesn't matter what you blow at it, it's in a vacuum. That being said, it might allow you to push it in tubes where the bulb will fail before the plate starts outgassing bad. The transmitter tubes that are forced air cooled have *external anodes*, which means some of the plate structure is out "here" in plain air. This allows the direct cooling of the plate with convective means, but also means you have a big piece of high conductivity metal with a couple thousand volts on it hanging out nearby.



I don't see that if you pushed a tube's dissipation by a few watts would it cause the envelope to fail, I don't think it wouldn't happen. If you kept the seals cool it would be fine besides damage done to the internals, ie plate outgassing. Of course the other problem would be the grid dissipation.

Ask George From Tubelab and he will be able to give much more info on the sudject then I can though.

An example I have pushed a 3c24 to a dissipation of 100 watts and all that happened was the getter material on the anode started to sublimate of and condense on the inside of the glass envelope.

And believe it or not the 3c24 is still functional
Nick
  Reply With Quote
Old 5th February 2009, 02:42 AM   #7
m6tt is offline m6tt  United States
diyAudio Member
 
Join Date: Aug 2007
I didn't mean to imply that the seals or envelope are going to blow if you push the current/voltage a bit . I just imagine that aircooling a glass tube would really only affect the envelope and not the anode so much...maybe you could mount the fan under the tube to cool the seals & maybe the plate a little through the pin. Probably wouldn't give you much.

I guess my example referred to tubes like the 6aq5, where I have a feeling the maximums are derated from 6v6 for reasons other than cathode size or arc-over, but because of bulb temp. It's just a hunch, maybe tubelab will blow some up someday and we'll see what the failure mode is
  Reply With Quote
Old 5th February 2009, 09:19 PM   #8
diyAudio Member
 
Join Date: Jan 2009
thanx gentlemen, interesting stuff
  Reply With Quote
Old 5th February 2009, 09:50 PM   #9
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Quote:
Originally posted by m6tt
I guess my example referred to tubes like the 6aq5, where I have a feeling the maximums are derated from 6v6 for reasons other than cathode size or arc-over, but because of bulb temp.
It is envelope temp, since the 6AQ5's wrap around anode is quite close to the glass.

Quote:
It's just a hunch, maybe tubelab will blow some up someday and we'll see what the failure mode is
He already did that, getting a 6AQ5 to put out some 30W. The glass melted.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 5th February 2009, 09:57 PM   #10
Banned
 
Join Date: Jan 2008
Blog Entries: 2
Valves operate by virtue of a temperature differential.

If the anode were as hot as the cathode then all other things being equal, their emissions would be equal.

The anode (in a glass valve) loses heat by radiation, and to a degree by conduction in some cases.

If the envelope is hot, it radiates heat back to the anode.

Not only does reduced envelope temperature reduce noise, it also improves valve life. A corollary of this is that it permits operation at higher anode dissipations. The problem is, how much?

You can get push-on valve heatsinks, you know.

w

Don't do it. Accept the improvement in valve life. If you want more power, build bigger.
  Reply With Quote

Reply


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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Very large forced air heatsink for sale mpmarino Swap Meet 5 27th November 2007 02:05 AM
For Sale: Fostex FE206E...forced sale Illusus Swap Meet 1 20th February 2005 01:38 AM
FS: Forced cooling tunnel webercarbmann Swap Meet 0 27th November 2002 08:50 PM


New To Site? Need Help?

All times are GMT. The time now is 07:51 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2