Paul,
Linear AM as the others have described is not very efficient, but it is
often convenient. For me, especially in the winter, it is efficient. Instead
of heating the shack with a 1500 watt resistance heater, I can talk on the
radio, and heat my shack at the same time with my linear. That is efficient!
With a little sophistication I could use the resistance heater, and with a
relay switching technique turn off the resistance heater whenever I am
transmitting. That way I won't overload my single 115vac 15a outlet in the
ham shack.
Your question about the Ranger is a good one. Just remember that the
6146
in the RF circuit is operating class C where the efficiency can be more than
twice that of linear running class AB, or B. Then the plate modulator is
varying the 6146 B+ at an audio rate. When the crest of the modulation
reaches 100% positive modulation, the 6146 B+ is doubled, and the current
therefore doubles. This results in the peak power to be 4X the carrier
value.
Another rule of thumb like what Patrick stated is that a Class C plate
modulated 6146 has a PEP output comparable to a single 811 in Class B linear
mode. So an Ameritron linear with 3 811's running AM linear at the limits of
the tubes is comparable to a Johnson valiant with 3 6146's in the final RF
amplifier. There is one big difference though. The 6146's won't be running
red, but the 811's will be. That is why several others recommend that with
linears we throttle back some to increase tube longevity. With this
de-rating to be easier on the linear, you could now compare the class C
Plate modulated 6146 to a linear amp using a single 813.
I run AM with a linear amplifier. I use a Gonset GSB-201 linear which
has
four type 572B tubes in parallel. This gives me a combined 640 watts of
plate dissipation. With 10 (carrier) watts drive from my Central electronics
20A (modified for QRO), I get 200 watts carrier from the Gonset, with
headroom to modulate upwards to about 125%. The 572b's only show a little
color, so I am not too worried. I do however produce a lot of heat, and this
can become unbearable in the summertime (no AC in the garage shack). Sigh.
I wonder if one could use a conduction cooled RF amplifier tube
attached to
a thermoelectric plate with the intent to cool a heat sink. Blow air past
the heat sink, and now the linear cools the shack! If you believe that, I
got some swampland in Arizona for sale...
Regards,
Jim
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Behalf Of RJ Mattson
Sent: Friday, December 19, 2003 11:18 PM
To: [email protected]
Subject: Re: [AMRadio] Looking for Linear Amp
Paul,
I believe, increasing your power from a 45 watt Ranger to 180 watts, is
just one "S" unit on most receivers.
Put your money into a good antenna.
bob...w2ami
----- Original Message -----
From: "Paul Sokoloff" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Friday, December 19, 2003 10:30 PM
Subject: Re: [AMRadio] Looking for Linear Amp
> Hello again,
> I had no idea I was going to stir up such an interesting discussion.
I
> was the person who originally posted this. After reading all of the
replies
> and as a newcommer to this, I have one question. If one needs an 800 watt
> amplifier to run 100 watts AM, then how does a Viking with 3 small 6146s
run
> 125 watts AM?
> I have a Johnson Ranger (45 watts with one 6146) which I wish to drive
> an amplifier for more output (maybe 125 to 150). Should I just get a
viking
> 2 or an amplifier? Does anyone have an amp they are interested in
selling?
> Thanks,
>
> Paul WA3GFZ
>
> _______________________________________________
> AMRadio mailing list
> [email protected]
> http://mailman.qth.net/mailman/listinfo/amradio
>
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