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: [email protected] 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:[email protected]
