[SBE] Certification note

[Mark Heller]

The 6L6 is a descendant of the "Harries Valve" developed by British engineer
J. Owen Harries and marketed by the Hivac Co. Ltd. in 1935. Harries is
believed to be the first engineer to discover the "critical distance"
effect, which maximized the efficiency of a power tetrode, by positioning
its anode at a distance which is a specific multiple of the screen
grid-cathode distance. This design also minimized interference of secondary
emission electrons dislodged from the anode.

EMI engineers Cabot Bull and Sidney Rodda improved the Harries design with a
pair of beam plates, connected to the cathode, which directed the electron
streams into two narrow areas and also acted like a suppressor grid to
absorb some secondary electrons. The beam design was also undertaken to
avoid the patents which the giant Philips firm held on power pentodes in
Europe. Because this overall design eliminated the "tetrode kink" in the
lower parts of the tetrode's voltage-current characteristic curves, which
sometimes caused tetrode amplifiers to become unstable, MOV marketed this
tube family under the sobriquet "KT", meaning "kinkless tetrode".

Because MOV's engineers did not feel the kinkless tetrode could be
successfully mass-produced, they licensed the design to RCA. This proved to
be a poor business decision on MOV's part. RCA subsequently had enormous
success with the 6L6. It replaced the use of power triodes in public-address
amplifiers almost overnight. So many applications were found for the 6L6
that a complete list would be impossible to assemble. MOV introduced their
version, the KT66, a year later.


The 6L6 Pinout, metal versions had the shell connected to pin 1RCA's first
version had a metal-canister shell rather than glass - being one of the
early octal base tubes, most of which were marketed as having metal shells.
Later versions, including the 6L6G, 6L6GA, 6L6GB, 5881, 5932, 7027, and the
final version 6L6GC had glass envelopes, which made radiation cooling of the
anode easier. The voltage and power rating of the 6L6 series was gradually
pushed upwards by adding features such as a micanol base, thicker plates,
thicker grid wires, grid cooling fins, and special ultra-black plate
coatings. The original metal version was rated for 19 watts dissipation,
while the later 6L6GC is usually rated for 30 watts.


----- Original Message ----- 
From: "John E. Beck" <wb0rxl at yahoo.com>
To: "sbe member discussion mail list" <sbe at sbe.org>
Sent: Thursday, November 15, 2007 7:49 AM
Subject: Re: [SBE] Certification note



> Is "B" the correct answer?

>

> Come on guys - don't leave me hanging!

>

> John E. Beck

> WB0RXL

>

> ----- Original Message ----

> From: "A9xw at cs.com" <A9xw at cs.com>

> To: sbe at sbe.org

> Sent: Tuesday, November 13, 2007 5:45:36 PM

> Subject: Re: [SBE] Certification note

>

> In a message dated 11/13/2007 4:54:15 PM Central Standard Time,

wgbw at lsol.net

> writes:

> >

> > and, I'm so old, I remember when we were asked to present possible

> > questions for the test... maximum ten questions per chapter!

>

> I bet they were good ones too!

>

> A 6L6GB is used as:

>

>       A. video modulator for high level TV modulation

>       B. audio amplifier power output

>       C. as a low distortion amplifier using screen grid feedback

>       D. all of the above

>       E. none of the above

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