Ed, I always admire those about to undertake such a project. I don't have a circuit for you, but I will share a few ideas. If you do use grid driven, it will likely need to be class AB1 (zero drive power to tube, i.e, just voltage), or class Ab2 where the grid draws a little grid current on modulation peaks. In either case, 25 watts will be way too much. Given the above choices, I'd use Ab1, and a passive 50 ohm grid input resistor, and scale the drive just short of grid current. Still you will need a grid bias supply, and screen supply in addition to a plate supply. That is a lot of stuff, but hey, why not if you want to do it?
Another approach, and I'm being a little simplistic here, is to think of a 4-400 in grounded grid as something similar to or about 4/5 a 3-500Z. A Heath SB-220 does legal limit AM with under 25 watts (carrier) of drive with two 3-500Z's in parallel G-G. No screen supply needed, and bias if necessary is easy with a power zener diode. So a 4-400 configured as a GG linear should be good for 150 to 200 watts am carrier output, and only need 10-15 watts carrier for drive. My figures are a SWAG, but I'd bet they are in the ballpark. Thanks for reading, Jim Candela WD5JKO --- [EMAIL PROTECTED] wrote: > I am planning to build a linear amp around a grid > driven 4-400 tube. Can > anyone suggest where I can find a suitable circuit > with component values. > I would like band-switching for 80, 40 and 20 > meters. I will be driving > it with a 25 watt carrier output rice box on AM. I > don't like the one in > the ARRL 1967 handbook because it requires you to > open the lid and > physically change taps on the coil and change tuning > capacitors. I don't > have any other older handbooks. Thank you. > > Ed K6UUZ > ______________________________________________________________ > AMRadio mailing list > Home: > http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net >
