Ve6fi Amateur Radio

4-1000A Linear Amplifier

This 4-1000A has been rebuilt a number of times over the last 10 years. Contest work can be very demanding. Like everything else one learns as time goes on and the design becomes firmer and more stable.  This amplifier will operate from 160 meters up to and including 15 meters.  The plate tune and the loading capacitors are vacuum variables. No arcing or sparking from these capacitors.

The coil stock is 3/16 copper tubing wound over high voltage insulating board.  The RF choke has one portion perpendicular to the other portion in order to overcome any self resonance occurring on the operating band. If it is resonant on one of the amateur band  you will have a choke fire! The axial blower on the top of the chassis is just to cool the band switch.



On the bottom of the amplifier you can see the filament choke, the tube socket, the input circuit chassis and various low voltage control power supplies. A vacuum relay is used on the output as well as the input of the amplifier.

Since we are driving this amplifier with just 100 watts care was taken with the input circuits to make sure that the input SWR was less than 1.2 to 1 on all bands. This allows you to drive the tube to full output with 100 watts of drive.



The 4-1000A tube is quit tall so you need a fairly large enclosure to accommodate it. This amplifier is run with 6.0KV on the plate so extra clearance is required to give the HV room. If you do not have enough clearance you will be getting your broom and sweeping up HV diodes.

The input circuit and output circuits are switched independently for simplicity.

The power supply for the amplifier is mounted externally in a 19 inch rack.  The power supply is simple and rugged. It uses a 2400 volt pole pig transformer, a voltage doubler, 32 microfarad at 9KV oil filled filter capacitors, step start contactors, protection bleeders, K2AW diodes and a circulating fan. Nothing fancy - just sturdy. This is a 13 db gain amplifier on 160 thru 20 meters and a 10 db gain amplifier on 15 meters.

Below are the component values and the output power.


Band Tune Load I grid I plate Power Out Gain db
15 35 pfd 923 pfd 50 ma .52 amp 1.0 Kw 10 db
20 30 pfd 285 pfd 90 ma .70 amp 2.0 Kw 14.7 db
40 65 pfd 560 pfd 100 ma .80 amp 2.0 Kw 13.8 db
80 115 pfd 810 pfd 100 ma .85 amp 2.0 Kw 13 db
160 270 pfd 1600 pfd 100 ma .85 amp 2.0 Kw 13 db