[AMRadio] Dentron Clipperton on am?..

[Gary Schafer]

Does your service monitor have an AM position?

The ALC is probably holding the peaks down. You may be running too much
carrier and the ALC won't allow 100% if the carrier is too high. As I
pointed out a few days ago the sum of the carrier voltage and the audio
voltage determine the peak power. If the radio is only capable of 100 watts
pep and the carrier level is too high you will hit the 100 watts PEP before
you get to the 100% modulation level. The ALC will start to cut back the
drive so you don't go over the 100 watt limit of the radio. Some ALC
circuits work a little different than others as to how they cut the power
back.

When using an amplifier,
Both the exciter and the amplifier together have to be capable of reaching
the peaks in order to achieve 100% modulation.

The amount of carrier that your amp can handle and still be able to modulate
100% will be 1/4 of the output that it is tuned up for. You will reach 100%
in either the positive or negative peaks set like that. You may hit the 100%
on positive peaks and not hit it on negative or it may hit it on negative
peaks and not on positive peaks. Depending on, here's that word again, the
"symmetry" of your voice.

I don't know that amp too well but I think that it is about a 1200 watt
output amp for SSB. So if it is tuned up at full carrier for 1200 watts out
then reduce the carrier to 300 watts for AM and don't change the tuning. If
you had 60% efficiency at full carrier you will have around 30% at the 1/4
power level.

I believe that the 572B has  160 watt plate dissipation. X4 gives you 640
watts of plate dissipation total. Input power with 300 watts out at 30%
efficiency will be around 1000 watts (300/.30= 1000). Subtract the output
power of 300 watts from 1000 and that leaves you with 700 watts that the
plates must dissipate. That is over powering the tubes by a little. I
wouldn't run more than 250 watts carrier out on it and maybe less as the
power supply may not be up to it.

So with 250 watts carrier out you should only apply enough drive so that
when you tune the amp for maximum output you have 1000 watts output. Then
reducing the carrier to 250 watts should put you within the rating of the
tubes.

Now this is all supposing that the exciter is not putting out over 25 watts
of carrier when the amp is putting out 250 watts. If the exciter output is
over 25 watts (assuming that it is 100 watts max) then it will not be able
to make 100% modulation before the ALC starts to kick in.

73
Gary  K4FMX



> -----Original Message-----
> From: jim and ella [mailto:wb5oxq at grandecom.net]
> Sent: Monday, April 18, 2011 10:49 PM
> To: garyschafer at comcast.net; Discussion of AM Radio in the Amateur
> Service
> Subject: Re: [AMRadio] Dentron Clipperton on am?..
> 
> 
> ----- Original Message -----
> 
> Subject: Re: [AMRadio] Dentron Clipperton on am?..
> 
> Acording to my Motorola service monitor my solid state exciter cannot
> reach
> 100% modulation.  At best I can only get 85% on the loudest peak and the
> average runs around 65-70%.  I am told I sound very good on am though.
> When
> I was running a
> titan amp and watching the peak reading led display it took 500 watts of
> carrier with the loudest modulation peaks to reach 1500 watts.  I
> damaged
> stereo equipment in the house running too much power so I sold the Titan
> to
> pay for the damage and bought a Clipperton because it should not be
> capable
> of that much power but 25 watts on am from the solid state exciter is
> not
> enough power to be heard under most conditions.  I find that lowering
> the
> power on the exciter to around 12 watts gives a higher average of
> modulation
> since the alc does not get involved at all.  MY main question was how
> much
> carrier can the 4 572B's run and have enough headroom left for
> moducation
> peaks?
> WB5OXQ.
>