Sander deWaal wrote:
"Andre Jute" said:


Andre Jute wrote:
Chris Hornbeck wrote:

On Tue, 16 Jan 2007 07:39:03 +0000, Eeyore
wrote:


In any event, an audible difference between DC and AC heating of DHTs indicates
to me that with AC there must be some signal modulation at 2 x line frequency,
like a tiny tremolo effect perhaps.


On the contrary, thermal time constant is too large for
heating to modulate emissivity even locally, and AC
heating is always used with hum nulling, which coincidentally
*exactly* (think carefully before disagreeing publicly)
also nulls all localized signal modulations.


The relevant circuits are at:
http://members.lycos.co.uk.cob-web.o...trafi-crct.jpg
http://members.lycos.co.uk.cob-web.org:8888/fiultra/T44bis-'Populaire'-crct.jpg

The hum nulling, for visiting siliconheads who clearly don't know
anything about tube circuits, consists of the circuit in the Western
Electric 300B cathode (that's the lower part of the tube, chaps) made
up of two 100 ohm resistors and the 100 ohm pot. (This has, amazingly,
already been described by Don Pearce in this thread as if it is merely
a feedback mechanism. Nor did Pearce enquire after its purpose...
Perhaps Pearce has negative feedback on the brain, because he also
twice described the grid leak resistor as a negative feedback network;
interestingly, none of the other siliconitis sufferers afflicting us
know enough about tube circuits to correct this gross error by
Pearce.)

The designs are discussed in these texts:
http://members.lycos.co.uk.cob-web.o...mp%20INDEX.htm


If you and Arny really want to play in our sandbox,
at least do your homework first.

They don't want to play in our sandbox. They want to **** in it, to
suck the jam from our doughnut, to drain the glee from our hobby. It
offends these grim witchfinders that we are having fun.


A copy to UKRA so Pearce can't say I knock him behind his back. -- AJ


Gotta give credit where credit is due, Andre, even if it is only 1 dB.
The 100 ohm potmeter, shunted by both 100 ohms resistors, provide a
very tiny amount of local cathode feedback.

I didn't say it wasn't *also* a feedback circuit to some
fractional extent. What I said was that the public
idiot Don "Bluster" Pearce mistook the AC humbuster circuit for
solely a feedback circuit, and missed its primary purpose. What I said
was that the public idiot Don "Bluster" Pearce mistook the grid leak
circuit for a feedback circuit. What I said was the public idiot
Don "Bluster" Pearce clearly knows buggerall about tube circuits
and should therefore keep his nose out of what he is totally
ignorant about. Bluster Pearce has run away now to shelter
behind his killfile, so the rest of us can get on with the business
of tubes.

- Maggies are an addiction for life. -

Coca-cola is cheaper.

Always wanted to say that...

Andre Jute
The definition of darwinian accident waiting to happen: Don "Bluster"
Pearce.