[AMRadio] AM Transmitter Advice??


Bob Bruhns bbruhns at erols.com
Fri Feb 17 11:23:27 EST 2006


12AX7s have surprised me with their power
capabilities before, but 20 watts output with 30
watts input is 67% efficiency, and that means that
the 20 watts output is the PEP output of the
3-12AX7 linear.  I think that the 10W rating with
a 6AG7 is PEP as well.

  Bacon, W3WDR


----- Original Message ----- 
From: "Jim Candela" <jcandela at prodigy.net>
To: "Discussion of AM Radio"
<amradio at mailman.qth.net>
Sent: Friday, February 17, 2006 7:29 AM
Subject: RE: [AMRadio] AM Transmitter Advice??


>
>
> Hi All,
>
>    I recently had a conversation with a ham in
San
> Antonio (forgot his call), and he told me that
he
> built a unique linear amplifier for his central
> electronics 10a, and for tubes he chose 3 type
12AX7
> in parallel grounded grid. He said he could run
30
> watts input (300v @ 100ma) with no problems, and
about
> 20 watts out. I find it odd though that a 10a
can do
> 10 watts with a single 6AG7, and 20 watts is
only a
> 3db boost.
>
> To my way of thinking, a linear amp needs to
boost
> your power at least 6 db (~1 'S' unit) to be
worth the
> trouble. For us AM'ers, going from 100 watts to
375
> watts carrier does not meet the 6 db boost
criteria,
> and that explains why a good antenna on a DX-100
is
> better than a average antenna on a Globe King
500.
>
> Still, as I once posted last year, a dual 304TL
> grounded grid linear seems to fit the bill as a
6 db
> 'brick' capable of 400 watts AM carrier output
with
> 100 watts AM input, or said another way it takes
400
> watts PEP and boosts it to 1600 watts PEP. There
was
> an old W6SAI construction project about this
(single
> 304tl GG amp), and I recall that the setup in
class C
> could run 1 kw dc input with over 1 kw rf output
> because of the low gain, and massive amount of
> feedthrough power from the exciter that finds
it's way
> to the output. This was a way around the FCC
power
> rules of the day.
>
> Regards,
> Jim
> WD5JKO
>
> --- Donald Chester <k4kyv at hotmail.com> wrote:
>
> > >Assuming one is going to build a linear, and
so
> > putting aside other issues
> > >such as linear vs plate modulation, why do
you
> > think it makes a difference
> > >what tube is used? Are you referring to
running a
> > linear at greater than
> > >legal limit?.
> >
> > Well, go ahead and try building a legal limit
linear
> > that runs a pair of
> > 807's in the final.
> >
> >
>
__________________________________________________
_____________
> >
> > This message was typed using the DVORAK
keyboard
> > layout.  Try it - you'll
> > like it.
> > http://www.mwbrooks.com/dvorak/
> > http://gigliwood.com/abcd/
> >
> >
> >
>
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