|[AMRadio] AM Amps|
ronnie.hull at glowbugs.com
Tue Jan 11 15:13:50 EST 2005
well all I can say is it works.. works well as a matter of fact, and has
been for 6 years :)
I typically run between 350 and 400 watts of carrier every day. It looks
great on the scope. Modulation envelope is perfect. 100% modulation. In 6
years Ive only lost one tube, and I accidently broke that one.
Ronnie - W5SUM
---------- Original Message -----------
From: Gary Schafer <garyschafer at comcast.net>
To: Discussion of AM Radio <amradio at mailman.qth.net>
Sent: Tue, 11 Jan 2005 14:34:26 -0500
Subject: Re: [AMRadio] AM Amps
> By "legal power out of the 813's" I assume you mean 375 watts
> carrier? If so there is no way the peaks are going to 1500 watts. A
> pair of 813's will not put out that much power in GG linear
> configuration. At least not very long.
> A pair of 813's in GG are good for about the same power out as 4
> 811A's. If you run them with more than 150 watts carrier out you
> will be flat topping with modulation, unless you keep the mod
> percentage very low.
> AT 375 watts carrier out at 33% efficiency that would require 1140
> watts plate input power. That would be a plate dissipation of around
> 380 watts per tube! Cooked to well done in minutes!
> Now if you tune them so there is higher efficiency, the plate
> dissipation will be lower, but then your mod peaks will never reach
> any where near 100%. Even if your driver is modulated 100%.
> In AM linear service the efficiency of the amplifier must be 1/2 as
> much for the carrier as it is for the peaks. This is how the voltage
> doubles to obtain that peak power needed.
> Without that ratio you will have distortion and splatter. As you
> noted when running 600 watts carrier out you must back the
> modulation down. At that power level you have almost no headroom at
> all for audio. You are at near maximum capability of the tubes with
> just carrier.
> Gary K4FMX
> ronnie.hull wrote:
> > This aint rocket science at my shack.
> > I have a pair of trusty old 813's in grounded grid with 3200 Volts on
> > plates. I drive them with my Ranger all the time with no problems at all.
> > I always tune the ranger up to full power into a either a dummy, or my
> > dipole. THEN switch the 813's into the line and then quickly dip the
> > It usually will dip back to about 80'mils. I leave it right there and
> > legal power out of the 813's.
> > If I want to bring the Ranger back up to full power, I can and it will
> > those 813's to 600 watts and sounds great.
> > I have been using this combination for 6 years and many of you have
> > on it.
> > If I DO bring the ranger back up to 120 mils, I have to be careful of
> > audio drive, as it will tend to start to distort if the gain is up to
> > But if I leave the Ranger at 80 mils, it works fine and I work coast to
> > Gotta love those old 813's!
> > 73's
> > de W5SUM
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