Linear Amplifier

This is a 160-10m "desktop kilowatt" linear amplifier using an Eimac 4CX1000A tetrode. It was developed between 1998 and 2002 by Mark G4AXX. After months of bench testing it was put on the air for the first time in the CQWW SSB contest 2002. Specifications Size 360mm(H) 270mm(W) 420mm(D) Weight linear 20kg + transformer 16kg AC Power 230V 13A Output Power 1400W PEP Input Power 25W/100W (switchable) Input SWR <1.5:1

• Click here for the amplifier design notes



• Click here for the schematic diagrams (PDF 100kb)

Soft-start timer board

Soft-start timer board and input contactor assembly

Tetrode Boards ^tm for more info visit http://www.ifwtech.co.uk/g3sek/

Front view of power supply deck

Front view of power supply deck with Alpha transformer in place

Side view of power supply deck. The Alpha transformer is at the back right hand side of the amplifier

The Bridge Board. This board connects the transformer secondaries to the Tetrode Boards ^tm and the Soft-start board

Rear view of the Power Supply deck showing the torroidal heater transformer below the mains input contactor assembly

Front-panel assembly showing voltmeter, ammeter, tune & load dial windows and power, reset and standby switches

Rear-panel assembly showing air filter, 230V mains input socket, isolator switch and bias adjust control. The RF input and output connectors on the RF deck fit through the holes at the top of the back panel

Rear-panel assembly showing fan (Papst RG-125)

Bottom view of RF Deck showing band-switch drive and load and tune capacitor drive shafts, and EHT wiring

Upside down view of air inlet to valve base, this mates with the exhaust port of the fan

Nylon gear reduction drive on the tune capacitor drive shaft

6:1 epicyclic reduction drive on load capacitor drive shaft

Side view of RF Deck. The tune capacitor is a Russian 21-850pF 5kV vacuum capacitor

Top view of the RF Deck showing the Pi-tank and the RF connector rear sub-panel

Overall top view of the RF Deck

Top view of the RF Deck showing the valve, anode RF choke and 10m section of the Pi-tank

The bandswitch from a WW2 BC375 transmitter, kindly given to me by Peter G3RZP. Recently 10 more of these switches have been bought and are available from

Pi-tank showing the 10kV DC blocking capacitor and the 10m coil

Close up of output RFC and N-type connection to the TR relay

Output coaxial relay (Tohstu CX520D)

Input relay, switchable 6dB attenuator and SMA connection to the valve base

Close up showing SMA RF input, heater, screen and grid connections to the valve base

Side/rear view of complete amplifier without covers

Left-hand side view of complete amplifier

Front/left-hand side view

Front view

Front/right-hand side view

Right-hand side view of complete amplifier

Rear view with attenuator switch and RF connectors showing through rear panel

Installation of Alpha "Unisil" power transformer

Right-hand side view with transformer

Close-up of right-hand side view with transformer

Top view of 4CX1000A

160m coil

15-80m coil

15m-160m coils and band-switch

15m-160m coils

EHT capacitor stack, Rectifier and Bridge boards. 90 degree drive shafts for tune, load and band-switch controls

Inside view of Soft-start timer baord, input contactor assembly, and heater and control transformers

Close-up of fan beneath the valve base

Top cover showing venilation holes

Top cover showing venilation holes

Amplifier with top and bottom covers

Front panel

Front panel

Front panel - eventually I'll paint the covers dark grey

- ready for the contests

Capacitor Board (9 x 220uF 400V)

Capacitor Board mounted on Power Supply Deck

Rectifier Board top side diodes

Rectifier Board bottom side, equalising resistors