>I notice George's first question is still unanswered.
>
>>two questions occurred to me while catching up on
>>my e-mail reading:
>
>>1: "gain is mu*rp" ??? how??? gain is "mu" isn't it?
>>i.e. Vout/Vin = gain = mu;
>>or... gain = gm*rp, but not a mixture of the two!
>
>>gain is dimensionless: mu is dimensionless:
>>gm is a (trans)conductance with the units of inverse
>>ohms: rp is expressed in ohms: gm*rp = dimensionless
>
>Let's define terms - we've got into enough trouble on this reflector by
>having words mean different things to different people.
>
> mu (amplification factor) is dVp/dVg (where d is a Greek delta,
>meaning a very small change). Similarly, gm (mutual conductance) is
>dIp/dVg and rp (plate resistance) is dVp/dIp..........Vp is plate
>voltage, Ip is plate current, Vg is grid volts.
>
>The signal voltage at the plate is Vin*gm* [ rp*rl/rp+rl] where *
>means 'times'.
>rl is load resistance and rp is plate resistance
>
>(I do wish you could guarantee e-mail to support equations!)
It's do-able. I draw equations with a drafting app., convert the file to
GIF format using Adobe Photoshop, and attach it to e-mail, with
compression-off. Using an Apple Macintosh OS, one simply drags the icon
for the received GIF file to the Newscape alias icon, and the GIF file
opens - - without further enrichment of the World's Richest Man.
>
>So the gain is Vo/Vin = gm* [ rp*rl/rp+rl]
>
>The model is a current generator of Vin*gm with two resistors, rl and rp
>in parallel across it.
>
>
>But gm*rp = mu so gain is mu*rl/(rp + rl)
>
>Does that clear it up George?
>
Some of the unclarity may be due to the use of 'Rp'. I associate the
term with the VHF parallel-equivalent resistance of the anode's
VHF-resonant circuit, and with the parallel-equivalent resistance of the
anode's VHF suppressor. . Others use the term to denote
"Plate/(anode) Resistance". The two terms are most definitely not
interchangeable.
- Basically, VHF voltage-amplification is Mu*VHF-Rp. IMO, more VHF
amplification is mo-betta if one is trying to build a VHF oscillator.
Rich---
R. L. Measures, 805-386-3734, AG6K
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