[Amps] "Tubes 201" - How Vacuum Tubes Really Work

[Chris Howard]

I don't have a dog in this fight.  I've enjoyed and appreciated
you guys educating me.

>From where things ended up, it looks like some body of 
people say that the grid fuse/resistor idea really works
and they are convinced their experience proves it.

There is another body of people that use reasoning/logic/etc
to say that it could never work.

I myself have a bit of a hard time with the universal
negative: "that will never work" type of argument.
But I appreciate that folks on both sides have a lot
more experience that I do.

The real lesson for me was that there is such a fundamental
disagreement on what is going on inside that little glass
box.  It definitely doesn't look like settled doctrine.
And that's OK with me, I can live with a little bit
of ambiguity.

The floating grid issue seems kind of intriguing.
Maybe I'll get out some old octals or something and play
around with that and see what happens. The "Tubes 201"
guy seems to go both ways, one sentence says never float
the grid, and the next sentence seems to allow for it.

73

Chris
w0ep




On Sun, 2006-07-23 at 13:04 +0200, Peter Chadwick wrote:
> Tom said:
> >Not quite a peer reviewed engineering text is it Will?<
> He does tell you not to leave grids open, though.
> When you have grid current, you have grid dissipation. Which is why tubes designed for Class C had carbon coatings or whatever to reduce emission. See the RCA TT4 Tube Manual. It's fair to say that flash over dumping a lot of current into the grid could well heat it enough to get emission.
> Whether 'arc' is the right term is arguable, in that 'arc' implies a plasma effect, which you don't get in a vacuum. However, 'flashovers' in high power tubes with a good vacuum have been written up many times over the years, with a number of explanations. In tube manufacturing circles, they were said to be 'barnacles', and could be removed by controlled energy flashovers - there was an article in about 1934 in the IEE journal. As I recall, flashovers are more prevalent with new tubes.
> Sorry, I just don't buy grid fuses ( and even more so, resistors as fuses) as a good idea. I believe I'm not the only one, though.
> 73
> Peter G3RZP
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