[AMRadio] Ranger... good news, bad news

EP Swynar gswynar at durham.net
Tue Nov 7 20:36:26 EST 2006

Hi Guys,

I haven't really been following this thread all that closely, but has any
mention been made yet about the fact that the MAXIMUM amount of RF output
carrier that one can safely extract from a linear amplifier tube in AM mode
is equal to ONE HALF of the tube's plate dissipation...?

Ex. an 813 has 125-watts of plate disipation --- in AM linear amplifier
mode, that'd translate to just under 65-watts of AM CARRIER output.

I used to run a pair of 813's in AM linear amplifier service for a total of
125-watts carrier output. A 'scope --- like a Heathkit SB-610 --- in
trapezoidal mode is absolutely invaluable in setting up an amplifier this

~73~ Eddy VE3CUI - VE3XZ

----- Original Message -----
From: "Gary Schafer" <garyschafer at comcast.net>
To: "'Discussion of AM Radio in the Amateur Service'"
<amradio at mailman.qth.net>
Sent: Tuesday, November 07, 2006 8:20 PM
Subject: FW: [AMRadio] Ranger... good news, bad news

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Jack Schmidling
> Sent: Thursday, December 07, 2006 5:49 PM
> To: Discussion of AM Radio in the Amateur Service
> Subject: Re: [AMRadio] Ranger... good news, bad news
> Gary Schafer wrote:
> >If you want to run 125 watts carrier out of the
> > SB200 on AM that means you need to tune the amplifier up for 500 watts
> a
> > little more output with the load and plate tune controls on the amp
> > for maximum output with a given amount of drive.
> Not sure I understand the why of this.  I did all as you suggested but
> found when I was done that the plate tuning of the amp was exactly the
> same as if I tuned it originally with the 100w carrier.  The dip was
> exactly in the same place and the loading optimum is so broad that no
> change could be noted.
> > Watching the scope on the output of the amplifier should show the
> modulation
> > peak voltage double what the carrier voltage is on the scope. If it
> doesn't
> > you haven't tuned up properly.
> Interestingly, the only way I get the peak voltage to double is with the
> ricebox.  I can never seem to get more than about 50% increase with
> modulation.
> js
> The peak envelope power of an AM signal increases by 4 times over the
> carrier power with 100% modulation.
> The linear amplifier must be tuned at the peak envelope power level or the
> peaks will never reach full power, the amplifier will flat top and
> and you will not sound good.
> How much drive power did you have when tuning up the amp?
> Were you using a rice box to tune the amp or the ranger?
> If you don't see the scope voltage double with modulation you haven't
> up right. If you adjust the scope to say 2 centimeters with carrier then
> modulation peaks should hit 4 centimeters.
> 73
> Gary  K4FMX
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