[Boatanchors] Using a SG-230 tuner on AM

Wed Aug 12 10:48:45 EDT 2009

Forgot to say that the power levels given here are all power OUTPUT levels. 
When the output power is reduced to 25% (400 watts to 100 watts) after tune
up, the input power will drop only about 50%. This is because the efficiency
is dropping 50% too and the net result is reduction in output to 25% of full
carrier tune up power.

73
Gary K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of Gary Schafer
> Sent: Wednesday, August 12, 2009 9:36 AM
> To: 'Carl'; 'D C *Mac* Macdonald'; boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Using a SG-230 tuner on AM
> 
> 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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> 
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