[Amps] Plate impedance

[Will Matney]

Jim,

Your correct. I thought it said plate impedance myself until I read what was in the book. What the formulas are about is the "Effective RF load resistance", and "Plate resistance". I have not yet seen anything in either RCA book about using the 1.8 factor though, and wonder where they're getting it from. In the RCA TT manual, they do list a table of K factors, but I haven't seen the plate impedance formula mentioned in there using them, unless I overlooked it. Matter of fact, I haven't seen it mention plate impedance where I've read. If I do find it, I'll post what it says.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 4/10/06 at 3:35 PM Jim Tonne wrote:

>The "plate resistance" equation is absolutely correct,
>and is used for small-signal amplifiers.  It is the slope
>of the curve at a given point.  It has nothing at all to
>do with the subject at hand, which originally was how
>to design PI networks. 
>
>> (1) "The plate resistance (rp) is the rate of change of 
>> plate voltage with change of plate current, and the grid 
>> voltage being maintained constant".
>
>Absolutely correct.
>
>I think we have again a case of "plate impedance" being
>confused with the load that the tube would like to see.
>The above-mentioned "plate resistance" is what you see
>when you look at the tube from the world, in a small-
>signal sense.  In the case of transmitter design, we want
>to know the  *load that the tube looks into*   which is a
>different thing.
>
>In the case of transmitter design, the load that the tube 
>looks into is quite generally much larger than the output 
>impedance ("plate resistance") of the tube in the case of 
>a triode, and quite generally much smaller than the 
>output impedance of the tube in the case of a tetrode or 
>pentode.  Rephrased, triodes look more or less like a
>voltage source and tetrodes look more or less like a
>current source.  In each case, however, they like to look
>into a specific value of load.
>
>- JimT