General > General Technical Chat
Re: My new 'Thorium' "Avitar/Icon" !!?
GlennSprigg:
Being a lover & enthusiast of old Valve/Tube radios and equipment, this is an element (No. 90) that was discovered to be VERY
useful, in adding to the Tungsten filaments/heated-cathodes to GREATLY increase the Electron emissions of these tube plates/coils! 8)
And would do so, at a much reduced/necessary temperature. Such filaments etc, became what was called 'Thoriated-Tungsten'.
The Thorium covering was only 1 Atom thick!! but that's all it took for 300-400% improvement in Electron emissions!
Thorium is a malleable silver colored metal, but slowly blackens under oxidization to Thorium-Dioxide (Th-O2) on the outside.
It is RadioActive, and interestingly... the most stable Isotope (232) has a Half-Life of over 14 Billion years!! which is slightly
older than the current calculated life of the Universe. It has/had many other uses in the past, and to-date. :scared:
bsfeechannel:
Nice choice of avatar. But let's take this opportunity to remember the humble barium, used on flashed getters. It easily oxidizes, capturing any air molecules left in the tube and turning white when the vacuum system seal totally fails.
helius:
The low work-function of thorium was also used to make brighter gas mantles for portable lamps. Once installed, the paper backing was charred away by the flame so only a microscopically-thin layer of thoriated graphite remained. After burning, they couldn't be removed without being destroyed.
mag_therm:
The old (WW2 era ) amateur operators in the club used to say about the thoriated tungsten transmitting tubes:
Do not apply plate voltage until the cathode filament is fully warmed up.
Do not allow long periods with heaters on and plate voltage off.
Both of these were related to the life of thoriated tungsten cathodes.
I was just of an age to have worked briefly on the 40 to 200 kW triodes before they went mostly obsolete.
Tubes were like the YD 1202 with a filament rating of 12.2 Volt 250 amp.
My notebook from 1984:
Storage : 2 years max without filament voltage
Transport and keep vertical
Conditioning: Apply Fil voltage for 15 minutes before HT on plate to reduce risk of flashover.
Thoriated Tungsten needs exactly T_cathode @ 2000 Kelvin
If V_filament 3% too high:
Filament power up by 5%
T_cathode up by 1 %
Emission up by 20%
Life down by 50%
The filament transformers had many taps to get the voltage in spec.
I recall there was a timer for delaying HT On, and a few other interlocks.
I don't think tha above applies to small consumer grade tubes.
The 6.3 V could have swings following the residential supply,
and the later ones had solid state rectifiers with plate voltage
instantly applied before the filamants warmed.
duckduck:
--- Quote from: GlennSprigg on December 01, 2020, 12:08:59 pm --- It has/had many other uses in the past, and to-date. :scared:
--- End quote ---
It was added (1%-2%) to electrodes for TIG welding. This was a thing in the 1990's, and I don't know if anyone still makes these. Having a little ionizing radiation sure helps start that arc easier. The big risk is from inhalation of the dust from grinding the electrode wire, which you have to do every now and then to keep a sharp tip on them.
http://files.aws.org/technical/facts/FACT-27.pdf
Navigation
[0] Message Index
[#] Next page
Go to full version