[AMRadio] info wanted on 4-400 linear amplifier


zuu6k at juno.com zuu6k at juno.com
Wed Aug 3 00:04:48 EDT 2005


Thanks, Jim.

Ed K6UUZ


On Tue, 2 Aug 2005 20:07:29 -0700 (PDT) Jim Candela
<jcandela at prodigy.net> writes:
> 
> 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
> --- zuu6k at juno.com 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
> >
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