Maybe this is why 300b's dont last as long - 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 2nd March 2008, 10:20 PM   #1
diyAudio Member
 
Join Date: Mar 2004
Location: Albury NSW Australia
Default Maybe this is why 300b's dont last as long

Hi
I contacted an Australian supplier of 300b's (Shuguan 300b-98's) and asked him about a few things re reliability etc. What he did say that compared to say old production 300b's the new ones dont have thoriated filaments and a) dont last as long and b) arent as emmisive because of this.
He mentioned that thorium kind of killed people in the factorys so I looked it up and well he may have a point there.
Thorium is indeed radioactive and can be used instead of uranium for reactors. It has a half life of 4 billion years or so.
So it seems that thorium may not be used in new tubes and if that is the case they wont emit for as long.
Dont break your tubes when they burn out as inhaling Thorium is not on my list of things to do.
It also begs the question... Tubes must give off radiation.
Hazard suit anyone?
Nick
__________________
"Better to say nothing and keep them guessing than to speak and remove all doubt."
  Reply With Quote
Old 2nd March 2008, 10:41 PM   #2
diyAudio Member
 
SpreadSpectrum's Avatar
 
Join Date: Nov 2007
Quote:
Tubes must give off radiation.
That's how they cool themselves.

Quote:
new ones dont have thoriated filaments
Are they oxide coated, then?
  Reply With Quote
Old 2nd March 2008, 11:22 PM   #3
diyAudio Member
 
Join Date: Mar 2004
Location: Albury NSW Australia
Default Must be

He didnt tell me what the new filaments are made of but one must assume they are oxide coated. With what I wonder?
__________________
"Better to say nothing and keep them guessing than to speak and remove all doubt."
  Reply With Quote
Old 2nd March 2008, 11:44 PM   #4
diyAudio Member
 
Join Date: Dec 2007
they could be just tungsten without thorium. thorium is added for emitting electrons at lower temperatures.
  Reply With Quote
Old 3rd March 2008, 12:43 AM   #5
OzMikeH is offline OzMikeH  Australia
diyAudio Member
 
Join Date: Mar 2007
You can still buy thoriated tungsten TIG welding electrodes.
The main thing is to use dust extraction when grinding them to a point.

If that is the case it might still be used in filaments. I expect you have to pay a lot extra.
__________________
Help some guys with funny hair bang two rocks together really hard.
http://athome.web.cern.ch/athome/LHCathome/whatis.html
  Reply With Quote
Old 3rd March 2008, 02:37 AM   #6
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Default Re: Maybe this is why 300b's dont last as long

Quote:
Originally posted by duderduderini
I contacted an Australian supplier of 300b's (Shuguan 300b-98's) and asked him about a few things re reliability etc. What he did say that compared to say old production 300b's the new ones dont have thoriated filaments and a) dont last as long and b) arent as emmisive because of this.
He mentioned that thorium kind of killed people in the factorys so I looked it up and well he may have a point there.
He's putting one over on you. Thorium isn't all that dangerous, and the fact is that they still use it to make the W/Th filaments for new production 845s, 813s, and other high voltage, DH RF types. As far as I can tell, 300Bs have always used oxide filaments since the type isn't rated for 750V+.

Quote:

Thorium is indeed radioactive and can be used instead of uranium for reactors. It has a half life of 4 billion years or so.
So it seems that thorium may not be used in new tubes and if that is the case they wont emit for as long.
More B.S. W/Th filaments are still used for new production 845s, 813s, 811As, and probably other types as well. So far as I can tell, 300Bs always used oxide filaments since they aren't rated to operate at voltages of 750V+, where you definitely need the W/Th since oxide can't stand up to that.

Quote:
It also begs the question... Tubes must give off radiation.
Hazard suit anyone?
Nick
Keep the operating potentials below 10KV, and you don't have to worry about it.

Whoever that supplier is he's putting a story on you, probably to unload inferior products so's you won't raise a fuss with him. Don't trust him, find another supplier, or, better still, a design that avoids the audiophool expen$ive boutique VTs.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 3rd March 2008, 05:38 AM   #7
Tweeker is offline Tweeker  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Cincinnati, Ohio
Pure tungsten filaments run very hot, if they had them the tube would be like a light bulb.

There are some, but it is usually for tubes that run at above 15,000V.

OSHA doesnt have a cow if I TIG weld with thoriated tungsten rods, and thats with a naked fuming arc, rather than sealed in a glass bulb
__________________
Be sure your foil hat has a good low impedance ground.
  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
dont be a mug dhole Pass Labs 1 20th April 2008 05:32 PM
* 35 watt * 300B SE = super 300B + Class A2 rick57 Tubes / Valves 4 13th July 2005 04:18 PM
Forgot to do this long long time ago chris ma Introductions 2 30th October 2003 10:53 PM


New To Site? Need Help?

All times are GMT. The time now is 07:57 PM.


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