Dave Plowman wrote:
In article ,
Nick Gorham wrote:

Secondly, if you look at the voltages on the fillament, one side will be
at a higher voltage than the other, by the heater voltage, no this means
that there is uneven bias along the length of the fillament, so I would
expect a uneven electron flow. Now I don;t know if thats actually taking
part in the difference, but I can't see how it can help. If you take a
extream example, of GM70 running at 100ma current, and the fillament
being connected via the normal two 100R resistors, the 20v filament
supply seemd to me to mean that o current flows in one leg, and 200ma in
the other.


The same applies to an AC heater. Only at 100 times a second. Nicely
inside the audio band. Be interesting to use HF AC - outside the audio
band - and see how it compares.


Yes agreed, but while I can't prove anything, it just worries me being
constantly one sided.

There are a couple of us intending to investigate the hf ac heating, so
we will see...

--
Nick