[ARC5] AM linear amplification

[Ian Wilson]

Good excuse to use a large tube (4-125, 813, etc). No need for air cooling
until you
get to one size of plate dissipation higher :)

73, ian K3IMW

On Mon, Dec 19, 2016 at 12:36 PM, Kenneth G. Gordon <
kgordon2006 at frontier.com> wrote:

> On 20 Dec 2016 at 9:05, AKLDGUY . wrote:
>
> >
> > My BC-AO-230 puts out about 5W and I'm interested in boosting that with
> a 6146B Class AB1
> > linear amp. The ARRL Handbooks say that AM linear amplification is
> similar to controlled
> > carrier modulation and caution that efficiency is low, about 33%, but
> don't give explicit
> > operating conditions.
> >
> > I assume that the (6146B) stage cannot at any time be driven to the same
> output that it is
> > capable of in SSB amplification. That's because with no audio applied,
> the level of the AM carrier
> > drive must be carefully set so that the tube's plate is dissipating half
> of its rated dissipation. The
> > application of audio drives the stage to a level where the plate
> dissipation is approached but not
> > exceeded. This level is far below the SSB PEP input.
> >
> > Anyone have any comments?
>
> I have nothing to add. You have about covered it.
>
> Using any linear amp in AM service requires keeping the plate dissipation
> at a "reasonable"
> level.
>
> You obviously understand that.
>
> I would expect no more than about 25 watts output from your amp. Still,
> that is 5X the
> un-amplified output. I think that would be well worth the effort.
>
> Actually, the 807 or 1625 has a slightly greater plate-dissipation rating
> than the 6146. Some
> books show it as having a PD rating about 5 watts greater than a 6146.
>
> In addition, controlled-carrier modulation has greater AVERAGE efficiency
> than straight AM,
> because the carrier falls to a much lower level in the absence of
> modulation, while it
> remains steady for AM.
>
> CC modulation of a 6146 results in around 35 watts output.
>
> Ken W7EKB
>
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