[AMPS] 4-1000A Configuration

[David A. Pruett]

John,

>From my experience, the numbers people have been tossing around here on the
reflector are correct.  If you run moderately high plate voltage (3000-4500
VDC) you'll see about 10 dB gain.  If you have a 200W exciter that might be
OK for 1500W out but watch the grid current.

Most of the guys I know with 4-1000As run grounded grid with lots of plate
voltage.  A popular configuration up here runs a power line pole xfmr (4800
VAC) which provides around 6400 VDC no-load out of a bridge.  This
configuration provides about 13 dB power gain, or output equals twenty
times the input.  This results in a very high plate impedance (> 5000 ohms)
which makes the plate tank design precarious above 14 MHz.  I have one
running well as a 40M monobander, but I've only known one guy to make it
operate well on 15/10.

Grounded cathode (or grid driven) will provide higher gain.  Basically, you
set the grid terminating resistance so that your desired driving power
develops the correct voltage swing from grid to ground.  The higher the
resistance, the less drive power required.  However, at high gains
stability can be difficult to achieve and neutralization will likely be
required.  If you really want to make an all-band 4-1000A amplifier for a
100W exciter, this is probably the most feasible way to go but it will be a
lot more complicated and require more engineering.

73,

Dave/K8CC

Home phone: (734) 481-0755
Home email: k8cc@ix.netcom.com
Work phone: (313) 493-2168
Work email: dap14@chrysler.com

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