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" <[EMAIL PROTECTED]> To: "Discussion of AM Radio" <amradio@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 <[EMAIL PROTECTED]> 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/ > > > > > > > __________________________________________________ ____________ > > AMRadio mailing list > > Home: > > http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > AMfone Website: http://www.amfone.net > > AM List Admin: Brian Sherrod/w5ami, Paul > > Courson/wa3vjb > > > > __________________________________________________ ____________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb >
