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RADARS Linear project

4m/6m 400W Linear

Circuit Diagram (Adobe pdf - 500k)

A low power 'baby' linear
Measuring 10" x 9" x 9"

Initial trials now completed: (August 2002): 
70MHz, 15W drive produced about 300W output.  260mA Ia at 2kV (520W in 300W out = 57% eff). 
Both PSU and PA ran cool on CW & SSB - (but my 150W dummy load got too hot and died !)

Small Modification needed for 50MHz. 
The PA efficiency is too low. Increase coil size (6 turns 28mm ID) and add switch for 70MHz. Switch from cold end and short 2 turns.
On test - 50MHz. 10W in produced 200W out.  180mA at 2kV (360W in 200 out = 55% eff). So still some room for improvement in PA coil design.
The 4/6m Linear
(not quite finished)
This is designed to tune from 50 to 70Mhz to cover both 4m and 6m.  Using a single Gi-7B it should give 400W output (continuous) for 15-20W drive.
Front view showing the SWR meter and the tune/load controls.  A grid tune control will be fitted in the bottom hole.  The single 12v 150mA fan should be enough to cool the valve under normal (CW/SSB) operating conditions.

Rear view showing grid fan inlet (12v Mini fan from PC CPU coolr), BNC for drive input and the locking DIN connector for heaters and HV (-ve). The floating coax on the right has a HV BNC connector for linking to the PSU. A PL259 plug will be fitted on the rear upper section for RF out

Internal view showing mounting arrangements.  The anode connection is made from a thin brass strip and the grid ring turned from brass (G4VVT).  The anode choke (on PTFE stock) is mounted directly onto a 680pF 10kV doorknob capacitor using a small turned brass ferule.

The grid compartment. The small CPU fan blows directly onto the heater/cathode connections which are again made from thin brass strip.
The copper wire for the coils is from 30A cooker cable.  the heater choke is wound on ferrite rod (from a scrap transistor radio).

Power meter / Bridge. Click
                                        for Circuit Diagram
A close-up of the SWR bridge from a design in the RSGB handbook.
Circuit Diagram.