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In Reply to: Ra and Rp posted by Andrew L. on March 30, 2007 at 00:17:48:
Usually written as little rp or ra to destinguish it from an actual resistor R. Little ra or rp is internal impedance of the tube whereas capital Ra would designate the (external) anode load resistor.Depends on what school you came from as to whether you use ra or rp - they are the same thing.
The little r is to remind you that it is a dynamic resistance (that is resistance to AC signal so purists would argue it should have been called an impedance) and it is calculated from the change in anode voltage that results from a change in anode current (so I would use symbol ra) - If you call the anode a plate instead then you probably use rp.
In algebra:
ra = delta Va / delta Ia
gm = delta Ia / delta Vg1
mu = delta Va / delta Vg1
So you can do all the algebra tricks to come up with
mu = ra / gm
etc.
Cheers,
Ian
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Follow Ups
- Re: Ra and Rp - Gingertube 00:31:59 03/30/07 (1)
- Ginger: About time someone laid it out in this thread... - Thomas Martens 21:12:10 03/30/07 (0)
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