[Boatanchors] Using a SG-230 tuner on AM

[Gary Schafer]

In a simple answer, the PEP will never be greater than full carrier power at
tune up.

With SSB with carrier AM the amplifier must be tuned for maximum PEP that is
expected. If you wanted to run 100 watts carrier you would tune the amp up
at 400 watts, reduce the carrier to 100 watts. The modulation peaks with
100% modulation will reach 400 watts just like with plate modulated AM. The
efficiency of the amplifier at 100 watts carrier level will be 1/2 of what
it is at 400 watts. In other words if the amp provides 60% efficiency at 400
watts, it will be 30% efficient at the 100 watt level. The additional power
output to make the 400 watts PEP in this case comes from the efficiency
change in the amplifier.
With this type of AM you can never get more PEP output than what the
amplifier is loaded to as it will flat top with over modulation.

With straight screen modulation (not controlled carrier) the modulated stage
operates very similar to the SSB linear amplifier. Tune up is done with full
screen voltage and then the screen voltage is reduced without retuning the
plate. Efficiency of the carrier is 1/2 of the normal efficiency when the
screen voltage is dropped. Carrier is typically 25 to 30% of what full power
out would be. Modulation peaks will go up to what the full carrier was at
tune up, 4 times resting carrier. This is often referred to as "efficiency
modulation". 
The extra power for the PEP comes from the efficiency change in the tube
with modulation just like it does in the above example with SSB AM.

Controlled carrier AM is similar to regular screen modulation except for the
carrier changing level along with modulation. Carrier levels can be run
lower with no modulation giving an apparent increase in efficiency but the
maximum output during tune up is the same as the PEP just like with regular
screen modulation or the SSB linear amp.

Many people mistakenly retune the amplifier for maximum output when reducing
the carrier for AM linear operation. It makes for more carrier power but
limits the peaks as the amplifier will quickly flat top with modulation. The
peaks have no where to go. 
The same applies to not reducing the carrier to 1/4 the output that the amp
is tuned up for. In other words tune the amp up for 400 watts output and
then reduce the carrier to 100 watts output. This allows for the 400 watt
peak envelope power to develop. If the carrier is only reduced to say 200
watts, the 400 watt PEP level will still be achieved with modulation but the
peaks will be clipped well before 100% modulation is reached and distortion
will result.

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of Carl
> Sent: Wednesday, August 12, 2009 8:45 AM
> To: D C *Mac* Macdonald; boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Using a SG-230 tuner on AM
> 
> Now that the noise has died down I'll get back to the original subject.
> 
> Ive not disagreed with the math, just the visible proof on my test
> equipment.
> 
> Im now perfectly satisfied with the 4X at least with 100% plate modulated
> Class C.
> 
> Now for today. How about controlled carrier screen modulation where there
> is
> no added modulator power to speak of?
> 
> Or SSB with carrier?
> 
> Carl
> KM1H
> 
> 
> ----- Original Message -----
> From: "D C *Mac* Macdonald" <k2gkk at hotmail.com>
> To: "KM1H Carl Huether" <km1h at jeremy.mv.com>;
> <boatanchors at mailman.qth.net>
> Sent: Sunday, August 09, 2009 3:26 PM
> Subject: RE: [Boatanchors] Using a SG-230 tuner on AM
> 
> 
> 
> Carl and otherson the boatanchors list:
> 
> I believe the SGC-230 is rated at 125 Watts PEP.
> 
> Since the Viking, DX-100, 32V-*, B&W, etc. ran
> close to 120 Watts carrier, 100% modulation would
> cause PEP output to be 400-500 Watts.
> 
> I don't believe it advisable to risk running that
> sort of power into the SGC.
> 
> I'm pretty sure most list members are aware of that
> fact but I believe that it bears refreshing.
> 
> 73 - Mac, K2GKK/5
> Oklahoma City, OK
> 
> 
> ----------------------------------------
> > From: km1h at jeremy.mv.com
> > To: boatanchors at mailman.qth.net
> > Date: Sun, 9 Aug 2009 14:30:11 -0400
> > Subject: [Boatanchors] Using a SG-230 tuner on AM
> >
> > Has anyone tried running a 100W output AM rig thru one of these?
> >
> > Id like to be able to be able to run a Viking I or II thru one using a
> 160
> > and 75M dipole in parallel for 160-20M.
> >
> > Carl
> > KM1H
> >=
> 
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