On Mon, 16 Mar 1998 09:04:27 -0700 John Lyles <jtml@lanl.gov> writes:
>I'm sure that this has been discussed and debated before, but here's
>about
>2 cents worth:
>
>As for those Eimac "Typical" ratings in the datasheets. I believe that
>those are normally the result of one of two things. Perhaps folks at
>Eimac
>had other approaches also, but my gut feeling was that they came up
>with
>these numbers like this:
>
>1) CPI/Eimac tested the tube in an amplifier, like the 4CX20,000A
>datasheet
>tested at 98 MHz in their own cavity. The typical currents were read
>from
>meters. These typical applications have a frequency quoted along with
>Pout,
>Pin, etc.
In more realistic sized tubes that the majority of this reflector is
concerned with I note that the Eimac sheets state "measured" and often
include a frequency. I would not expect them to actually measure every
tube in their repitoire.
>2) Chaffee analysis (fourier series reconstruction of the DC currents
>using
>the tube curves, a la Eimac tube computer #5). This is strictly a DC
>analysis, so it neglects the RF effects such as ceramic heating,
>conductor
>losses, electron transit effects at very high freq, etc. This is more
>typical of how "Typical"
>currents came about. It is usually stated "RF Amplifier Operation" and
>no
>freq is given.
In the tubes that have been the topic of discussion recently the maximum
frequency AND the measured frequencies are often given. They also include
power delivered to the load. Where the measured frequency is not given
Eimac uses a "up to xxxMHz" which is considerably below the maximum.
Do you have any additional data on tubes that are confined to the 500W to
2.5KW useable output range?
>The grid dissipation is the important maximum rating to stay under.
>I'd be
>surprised that there was a grid current limit as well, if the grid
>dissipation max was quoted. Plate current is sometimes listed as a max
>rating, only because it is closely related to max cathode current
>which is
>limited by the cathode or filament emission.
Maximum Ig is not published in the spec sheets when dissipation is...I
certainly agree.
As mentioned in an earlier post I suspect that the maximum grid current
ratings were strictly for the amp manufacturers operator manuals and
contain a considerable safety margin. If you note the amount of space
that has been taken on this reflector without any solid agreement on
dissipation vs grid current ratings you can then imagine the abilities of
the" typical" Joe Sixpack ham amp user.
73 Carl KM1H
>John
>K5PRO
>
>
>
>
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>
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