N
Nelson
Guest
"JP" <johnpowers6@cox.net> wrote in message
news:V5iYk.7644$st1.4757@newsfe10.iad...
the computer to get out of it.
Nelson
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news:V5iYk.7644$st1.4757@newsfe10.iad...
Nelson
H
Heinz Schmitz
Guest
John Byrns wrote:
When the anode voltage is applied to the cold tube, the cathode during
heating up is operated in the saturation region. i.e. it cannot emit
as many electrons as could be drawn off.
It is said, that this can damage the cathode.
Why else would we find many devices where a relay does just that:
Switch on anode voltage only after the cathode is properly heated?
Just because of nice to have or to avoid start-up hum?
Regards,
H.
My present understandig:So does anyone have a comprehensive explanation of this cathode warm up issue,
for both low power and high power tubes?
When the anode voltage is applied to the cold tube, the cathode during
heating up is operated in the saturation region. i.e. it cannot emit
as many electrons as could be drawn off.
It is said, that this can damage the cathode.
Why else would we find many devices where a relay does just that:
Switch on anode voltage only after the cathode is properly heated?
Just because of nice to have or to avoid start-up hum?
Regards,
H.
H
Heinz Schmitz
Guest
Michael A. Terrell wrote:
the triode part is deaf, whereas the heptode part still works fine?
One may assume, that the triode (oscillator for AM) was mainly
left without current, because people preferably listened to FM.
Why do tubes go?
Obviously what goes is the cathode. Obviously it does not burn,
like the wires in light bulbs. It loses the ability to emit. Now why
is that?
Regards,
H.
Is it not funny, that in many old tube radios you find ECH81, where- heating before applying anode voltage,
- avoiding long periods without anode current,
Useless on low power vacuum tubes that are not used in some bizarre
circuit. Its a different matter on high power transmitter tubes.
Your kind posting shares a property with many usenet postings:
It provokes the most valuable question: "Why?".
Why, what? Have you ever seen any provable problems with low power
receiving tubes, or ar you just another tube freak repeating fairy tales
and folklore? Do you have decades of real experience with all types of
vacuum tubes behind you, or are you YAKIAH?
the triode part is deaf, whereas the heptode part still works fine?
One may assume, that the triode (oscillator for AM) was mainly
left without current, because people preferably listened to FM.
Why do tubes go?
Obviously what goes is the cathode. Obviously it does not burn,
like the wires in light bulbs. It loses the ability to emit. Now why
is that?
Regards,
H.
J
Jim Mueller
Guest
Tubes with pure tungsten filaments don't have to be preheated. They
don't have any coating or other material alloyed with it to damage.
Tungsten filament tubes can be run in emission-limited mode with no
problem; some are even made to be used this way. Examples are the 1236
and 2AS15. Tungsten filaments are also used in vacuum gauge tubes
because they aren't hurt by being exposed to air (when cold).
Pure tungsten filaments are used in very few tubes because they are
inefficient and have short life because of their high operating
temperature (they glow bright white).
Tubes that we are likely to encounter with pure tungsten filaments are
old ones like the 01. The inefficiency of these filaments can be seen
from the data sheets for these tubes. They take 5V at 1A whereas the
thoriated tungsten version, 01A, is 5V at 0.25A. Oxide coated filaments
are even more efficient; the 01B is 5V at 0.125A.
Heinz Schmitz wrote:
Jim Mueller wrongname@nospam.com
To get my real email address, replace wrongname with dadoheadman.
Then replace nospam with fastmail. Lastly, replace com with us.
don't have any coating or other material alloyed with it to damage.
Tungsten filament tubes can be run in emission-limited mode with no
problem; some are even made to be used this way. Examples are the 1236
and 2AS15. Tungsten filaments are also used in vacuum gauge tubes
because they aren't hurt by being exposed to air (when cold).
Pure tungsten filaments are used in very few tubes because they are
inefficient and have short life because of their high operating
temperature (they glow bright white).
Tubes that we are likely to encounter with pure tungsten filaments are
old ones like the 01. The inefficiency of these filaments can be seen
from the data sheets for these tubes. They take 5V at 1A whereas the
thoriated tungsten version, 01A, is 5V at 0.25A. Oxide coated filaments
are even more efficient; the 01B is 5V at 0.125A.
Heinz Schmitz wrote:
--John Byrns wrote:
So does anyone have a comprehensive explanation of this cathode warm up issue,
for both low power and high power tubes?
My present understandig:
When the anode voltage is applied to the cold tube, the cathode during
heating up is operated in the saturation region. i.e. it cannot emit
as many electrons as could be drawn off.
It is said, that this can damage the cathode.
Why else would we find many devices where a relay does just that:
Switch on anode voltage only after the cathode is properly heated?
Just because of nice to have or to avoid start-up hum?
Regards,
H.
Jim Mueller wrongname@nospam.com
To get my real email address, replace wrongname with dadoheadman.
Then replace nospam with fastmail. Lastly, replace com with us.