I appreciate all of the suggestions. I'm not locked into a particular tube configuration yet, but I have to admit there is something appealing about running the 450TH. It's probably my mental image of two of them lit up behind a glass window in the front panel :)
Clay W7CE ----- Original Message ----- From: "John Coleman, ARS WA5BXO" <[EMAIL PROTECTED]> To: "'Discussion of AM Radio'" <amradio@mailman.qth.net> Sent: Sunday, October 03, 2004 12:37 PM Subject: RE: [AMRadio] Home brew AM Cathode modualtion > The "Rice" neutralization circuit works better with a higher Q > grid tank and, if possible, some input swamping or grid load resistor. > The biggest trouble with the circuit is that the loading of the grid > tank is not constant over the full RF cycle as a result the "Q" and > balance is shifted somewhat over the period of the RF cycle. Starting > with a higher "Q" or C value is one way of minimizing this effect. > > The circuit does work because I used it as well and also with a 304TLs, > back in the days of experimenting with the ultra modulation or balanced > high level modulation circuits. I eventually went to standard "Push > Pull". > > John, WA5BXO > > > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Donald Chester > Sent: Sunday, October 03, 2004 12:45 PM > To: amradio@mailman.qth.net > Subject: RE: [AMRadio] Home brew AM Cathode modualtion > > > >The 450th is a big triode, so I don't think you can run it single ended > pie > >net output, you would need to do 2 250th tubes in push pull or > something, > >but the 450th would do the cathode modulator quite well. > > > You could use a single-ended pi-network type output circuit, with a > balanced > grid tank coil. That is knows as "Rice" neutralisation. You don't get > as > perfect null as you can with a balanced plate tank cincuit or a pushpull > > arrangement, but it works well enough that it became the standard design > of > tube type broadcast transmitters starting in the late 50's. > > I used that circuit with the first high power rf final I ever built, > using a > 304-TL in the final, because I didn't have a large split stator tuning > capacitor on hand. > > Don K4KYV > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net
