[AMRadio] Legal limit AM amplifier, homebrew

[Bernie Doran]

Yep, yep. A lot of the older tubes have a lot of internal capacitance and 
and long lead lengths that become difficult to get on even 15 meters. now a 
few were easy, such as the 100 Ts and 250 Ts. They are pretty rare.  no 
problems with 40 and 80 meters however with just about anything.
----- Original Message ----- 
From: "Rob Atkinson" <ranchorobbo at gmail.com>
To: "Discussion of AM Radio in the Amateur Service" 
<amradio at mailman.qth.net>
Sent: Sunday, November 13, 2011 11:10 AM
Subject: Re: [AMRadio] Legal limit AM amplifier, homebrew


It is my understanding that 833s don't do well in the higher HF bands.
 I can't quote chapter and verse--I just recall being told that by one
or two people I trust as far as their competence is concerned, i.e.
they were long time techs and AMers who knew what they were doing.
But, if you only care about the low bands (that's all I care about)
then there's no problem.

One of my points in my earlier message about power that probably
didn't come out very well is that people new to AM get so focused on
the 375 watt nonsense that they miss other things that are far more
important and much more likely to get a new AM op in trouble, like
wildly overdriving the audio on a rig like a DX100, running it
directly into a fan dipole with a signal 20 kc wide and appearing on 3
bands, all at the same time.  things like that get folks into trouble
1000 times more often than some guy with a very pure clean 400 or 500
watt broadcast rig with tight sidebands and good distortion free
audio.

73

Rob
K5UJ

On Sun, Nov 13, 2011 at 8:06 AM, Rick Poole <wa1rkt at arrl.net> wrote:
> Thanks to all for all of the wealth of information you have here.
>
> So, it sounds like a reasonable amp would be a pair of 833's in
> push-pull running class B linear for AM and class C for CW, and
> perhaps forget the high-level plate modulation idea. 1500 watts
> output on CW and, as a starting point, shoot for 375 watts carrier
> out on AM for 1500 watts PEP at 100 percent modulation. I have read
> K4KYV's paper on "The 375-Watt AM Carrier Power Myth" and more or
> less understand the issues, but 375 watts carrier out on AM sounds
> like a good starting point until I understand the issues a little better.
>
> Bernie makes a good point that the difference between such an amp and
> the barefoot output of the DX-100 on AM probably will be just barely
> noticeable, if at all, on the other end. The DX-100 is rated 100-125
> watts out on AM, and there is a general guideline that says if you
> can't increase power by at least a factor of 4, it's rarely worth
> it. For CW, though, it will make a significant difference. Plus it
> gets mighty cold here in the shack in the winter and I need something
> to keep the place warm. :-)
>
> 833's at least seem to be available... RF Parts has Taylors for
> around $120... hope they last longer than the Chinese 811A's and
> 572B's do... :-(
>
> Now... where's a good place to get a power transformer and filament
> transformer for such a beast?
>
> Rick WA1RKT
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