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PAGE 16
This section is a continuing technical treatise on the workings of Irish Pubs but to make it easier for the layman to understand, it is
explained in terms of vacuum tube technology. Enter the original bar - free beer and no doors. Well, it turns out that some control over
the flow can be a necessary and useful advantage. This led to the invention of those swinging louvered saloon doors which are open
at the top and bottom. They are patterned after the control grid of the vacuum tube, which is a loosely wound coil of thin wire located
between the cathode and the plate.
In a Triode the plate is always positively charged with high voltage D.C. and even though the grid is blocking the path, those negative
electrons can still FEEL the strong attraction - just as the Irishmen can see in through the louvers of the bar doors. They know what
pleasures lie beyond, but to get there requires overcoming the negative influences controlling the access. This negative influence is
typically called a Bias. In electronic terms that means the grid is supplied with a voltage which is slightly MORE NEGATIVE than the
already negative electrons. The more negative the Bias, the more it tends to neutralize the attraction of the plate and repel the
electrons back toward the cathode.
The Irish can be similarily charged with Bias, but unless you are Irish yourself, this type of Biasing may be more difficult to understand.
The effect is similar though: The more negative the Bias, the more it impedes forward progress. Generally speaking though, the
electronic Bias of the grid is easiert to overcome, and for two main reasons: First, the Bias is set - like the bar doors - to allow some
passage. Second, the grid is mostly NOT THERE, like the louvered doors which are mostly open spaces. Unlike the plate which is
solid, the grid is like a coiled bed spring. It can create a repelling field but mostly it’s empty space in between widely seperated
windings of wire. It’s very easy to control the electrons as they pass through the grid’s force field: Changing the grid voltage only
slightly will have an enormous effect on how much current flows through... and that’s what AMPLIFICATION is: a small change in
voltage at the grid causing a large change in current flowing to the plate.
The purpose of the louvered bar doors is similar to that of the grid, namely, to give momentary pause while still revealing the promise
within. Hesitation mostly gives way to temptation, but there are those few stalwart Irishmen who think twice and decide to come back
later. Most just pause slightly then go on through. That is the purpose of the bar doors: to prevent everyone from crowding in all at
once - and as the door is made less of a barrier, wider spaces between the louvers, more of the bar’s attractive influence is felt outside
thus amplifying the customer flow and increasing the crowd at the bar.
6 - 1 TRIODES:
SCREEN
GRID
GRID
CATHODE
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Structure of a 6L6 / 5881
Beam Power Pentode.
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BEAM-
CONFINING
ELECTRODE
PLATE (+,+)