Jim,
I read this over again last night, and it didn't mention anything about triodes
only. The main reason I posted this was to show the differences, plus find
where the illusive 1.8 came from in print. So far, the only book I've seen 1.8
listed in was Bill Orrs Handbook. I don't have any newer ARRL handbooks past
the 90's as they seemed to be the same old thing, over and over, with not that
much new.
Here's the thing. I use 1.8 just like evryone else because it does get you
there. I calculate the plate current though the same way it was shown in this
volume of the ARRL Handbook, by efficiency. I seen in the old RCA Radiotron
handbook where it said the plate current for class AB could be as much as 3
times. How they come up with this, I don't know as efficiency is efficiency.
Everything I've read says AB is around 60% efficient, not less. To my opinion,
there's a lot of mis-information out there as compared to what I've seen work
in the real world. I would like to find out though where the factor of 1.8 was
first mentioned.
Best,
Will
*********** REPLY SEPARATOR ***********
On 4/11/06 at 9:04 PM jkearman@att.net wrote:
>From: "Will Matney" <craxd1@verizon.net>
>> Class AB, K = 1.5
>
>My understanding is that this value of K applies to triodes, where Ep can
>swing nearly to zero. For tetrodes, Ep cannot swing below the screen
>voltage. IIRC, this has the effect of increasing K.
>
>It's useful to consider the consequences of slight errors in
>component-value selection. Assuming your variable controls (plate tuning
>and loading) have enough range to get a close match, the negative
>consequence would be a Q different from what you calculated. But if you
>give yourself enough range in tuning and loading Cs, you should be able to
>tune for _best linearity_ (more important than best efficiency) and still
>get enough Q to reduce harmonics below FCC requirements.
>
>If you calculate a range of plate loads by varying K from 1.5 - 1.8, and
>then calculate tank circuit values based on a Q range of 12-15, you should
>come up with tuning and loading cap values that will do the job.
>
>73,
>
>Jim, KR1S
>http://kr1s.kearman.com/
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