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Re: [Amps] LDMOS availability

To: amps group <>
Subject: Re: [Amps] LDMOS availability
From: Jim Garland <>
Date: Fri, 9 Jun 2017 22:02:53 -0600
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There are two issues, here, one being the definition of Class C, and the other being linearity. I'm inclined to agree with Bill on both. It's not hard to imagine modulating the bias, so that on voice peaks, for example, the amp moves in the direction of Class B, but regresses to Class C at low drive levels.In that case, the class of operation varies with the drive. That said, Class C is by definition non-and that occurs whenever the device doesn't conduct over a full RF cycle.

I have a homebrew amp with two-tiered bias. On SSB, in pauses in speech, the amp is biased at a very low resting current (approaching Class C) to cut down on heat, but on voice peaks where the linearity is needed, it switches to Class B. One has to be careful playing that trick, however, to avoid switching transients.


Jim W8ZR

On 6/9/2017 8:59 PM, Bill Turner wrote:
------------ ORIGINAL MESSAGE ------------(may be snipped)

On Fri, 9 Jun 2017 20:56:33 -0400, Mark wrote:

But the bottom line is simply that if the device conducts less than 180
degrees it is class C.  If any method at all can be used to increase
linearity this does not change the class of amplifier, it just improves the

Nonsense.  If the amp conducts less than 180 degrees it can not
possibly be linear because the output in NOT a replica of the input.
That's the definition of "linear".

If you "modulate" the bias to make it linear, it is no longer Class C.

Don't try to make things more difficult than they are. What you were
taught years ago was and is correct.

73, Bill W6WRT
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