BOTH the imaginary Conventional current and real current are necessary
when analyzing some circuits.
The Imaginary current makes analyzing a solid state schematic much
easier, even if in reality it doesn't work that way.
As engineers use conventional current (I have run into some that didn't
understand real current) I think conventional current will be around for
a long time.
73
Roger (K8RI)
On 10/26/2016 Wednesday 3:39 PM, Gene May wrote:
All,
Concur with Bill W6WRT re "positive vs negative" convention in describing
current. The convention we use now is left over from at least a hundred years ago when a
scientist guessed wrong about the polarity of the electron. To me, thinking in terms of
the direction of electron movement is far more clear.
Suggestions by Bill and Gary K4FMX and others to put a resistor from the screen to the
cathode, such that the resistor will pass at least the maximum "negative
current" (meaning the screen is emitting electrons) that the screen will pass will
work fine. This is absolutely essential if the screen grid supply is series regulated.
Zeners connected in this way (a way to parallel regulate the supply) should pass at least
the same. A little extra current flow is a good idea.
Suggest finding a copy of the Eimac publication Care and Feeding of Power Grid
Tubes, out of print but easy to find used online from used book dealers or at
hamfests.
I am using a power supply for tetrodes designed and sold by Ian GM3SEK, which
regulates screen current very well. Ian can be found on this.
Gene May WB8WKU
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To: amps@contesting.com
Subject: Amps Digest, Vol 166, Issue 26
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Today's Topics:
1. Re: Negative current with a Zener screen grid regulator (Bill Turner)
----------------------------------------------------------------------
Message: 1
Date: Sat, 22 Oct 2016 18:55:25 +0000
From: Bill Turner <dezrat@outlook.com>
To: Amps group <amps@contesting.com>
Subject: Re: [Amps] Negative current with a Zener screen grid regulator
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------------ ORIGINAL MESSAGE ------------(may be snipped)
On Tue, 18 Oct 2016 05:44:13 -0600, W8ZR wrote: >Positive screen current means
that current flows into the grid, and negative screen current means that current
flows out of the grid.
REPLY:
Be careful with this "into" and "out of" business. He is talking about the
so-called conventional current, which exists only in the imagination.
In the real world, positive screen current (electrons) flows from the cathode
to the screen and out to the positive power supply. Likewise, negative screen
current means the screen is actually
emitting electrons as if it were a cathode itself, a phenomenon caused by secondary
emission where arriving electrons actually "knock off" electrons from the
screen and it appears to be emitting electrons of its own. See Wikipedia discussion:
https://en.wikipedia.org/wiki/Secondary_emission
Because of this phenomenon, the screen supply must be capable of supplying
electrons as well as receiving them. This is most easily accomplished with a
resistor from screen to ground, whose value is such that current through at
idle equals or exceeds the value of expected negative screen current.
I wish the concept of "conventional current" would disappear from the textbooks
since it purely imaginary. Electron flow is real.
73, Bill W6WRT
------------------------------
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