----- Original Message ----- Subject: [AMRadio] Building Date: Tue, December 4, 2007 13:53 From: "jeremy-ca" <[EMAIL PROTECTED]>
> Ive been wondering, besides the drive requirement, why swamped grid cant be > used in Class C? It would eliminate the neutralization requirement with some > tubes as well as the hassle of a bandswitching input. > I was attracted to this design in the original incarnation of the RF deck for my PDM transmitter - at the time it was a class C final using a single 4-400. To get enough grid drive I was trying to use (IIRC) a 16:1 Guanella transformer design out of Jerry Sevick's book, for a 4X voltage step-up from a 50 ohm source. Worked acceptably except at the edges of the intended frequency coverage (160M & 10M), where the VSWR was out-to-lunch, even into a purely resistive load. Also, as I recall, 15M was sort of marginal. Once the parasitic reactance of the grid circuit was added, of coarse, things got even worse. I'm not saying it can't be done, but I couldn't get it to do what I wanted with a reasonable amount of effort expended. So I went to a variable T-network input and swamped the grid with about 3000 ohms non-X (in fact I bought the resistors from Radiokit!). More knobs to twiddle, but worked much better for me. Same input circuitry is in place now with a pair of 7527A's. 73, -Larry/NE1S ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected] To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
