Heaters & Filaments: AC vs. DC

[DF96]

This thread is rapidly descending into Alice in Wonderland territory. I will sit on the sidelines for a while and see if people recover their composure.

[SpreadSpectrum]

Is it me or is this thread getting a little too...heated? Sorry, couldn't resist.

[SpreadSpectrum]

Originally Posted by DF96

This thread is rapidly descending into Alice in Wonderland territory. I will sit on the sidelines for a while and see if people recover their composure.

That's to be expected when the initial quote was pulled straight out of the rabbit hole.

[nazaroo]

Originally Posted by SpreadSpectrum

Is it me or is this thread getting a little too...heated? Sorry, couldn't resist.

resist? was that a pun?

This thread began with AC/DC, so I guess the dude look like a lady was no real surprise.

I hope speech impediments don't get traced to TV exposure.




http://www.youtube.com/watch?v=kQFKtI6gn9Y

[trobbins]

I suggest the issue relating to swapping the DC polarity is related to the contact interface between power supply and tube terminals, rather than any internal parts of the valve. And it may well be that heater tube terminals for such Tx types are substantially different from anything 'we' normally come across, and operate in a substantially different temperature environment and at different voltage levels. But worth eeking out some more background understanding.

[popilin]

Gentlemen (sorry to call them so, but still do not know)
I regret to say that I was mistaken when I thought I was wrong.
What I said in post # 3 is correct, I was wrong when I apologized in post # 7
I have checked my calculations and are correct.
Excuse the quality of attachments, were made with MathType, and the only way to upload that came to mind was this.


For an Ideal loop where an AC current i(AC) flows with a voltage U(AC), from equation (20), the AC magnetic field is given by

B(AC) = [ U(AC) x 10^8 ] / [ sqr (2) * (Pi) * S * f ]

Clearly only depends on the AC voltage, not AC current.


For an ideal loop where a DC current i(DC) flows with a voltage U(DC), from equation (28), the DC magnetic field is given by

B(DC) = [ 4 * (Pi) * u * i(DC) ] / ( c * l )

Clearly only depends on the DC current.

The confusion of some members of the forum, lies in the fact that whenever we have a current, we also have a voltage, and vice versa.

[popilin]

Originally Posted by Chris Hornbeck

Not certain whether it applies to audio sized valves, but TV transmitter finals' filaments are fed DC and incorporate an automatic polarity switch at (the rare) turn off-on's. The reason was explained to me as a valve life issue. Might be true...

A clever person on DIYAudio posted that the same could be accomplished in a stereo amplifier by wiring the two channels' valves in opposite polarity and switching between from time to time. True genius is simple, ain't it?

Thanks,
Chris

Hi Chris
The valve that you refer, is directly heated cathode?

Best regards
Johann

[Chris Hornbeck]

Originally Posted by popilin

Hi Chris
The valve that you refer, is directly heated cathode?

Yes, great big expensive things that are actually *rebuilt* when worn out. I doubt many stations still use electron valves - most, as I understand it, now use multiple paralleled solid-state amplifiers - but even ten years ago the big tungsten filaments still walked the Earth.

All good fortune,
Chris

[popilin]

Originally Posted by SpreadSpectrum

Is it me or is this thread getting a little too...heated? Sorry, couldn't resist.

Only now I understand your joke. Genius!!! LOL
I think too slowly, right?

Best regards
Johann

[popilin]

Originally Posted by Chris Hornbeck

Yes, great big expensive things that are actually *rebuilt* when worn out. I doubt many stations still use electron valves - most, as I understand it, now use multiple paralleled solid-state amplifiers - but even ten years ago the big tungsten filaments still walked the Earth.

All good fortune,
Chris

I think I know the cause of the reverse polarity of the filament / cathode.
If the filament/cathode is powered with DC, one half has less(more) emission than the other, and aging is uneven, so reversing the polarity happens the other way around.

Best regards
Johann