The VK4YE 1 Kilowatt Linear Amplifier.

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Plate Choke.

The plate choke was made using a 150mm length of standard 20mm pvc conduit wound with 0.4mm enamelled wire. About 320 turns gave a winding length of 125mm which was terminated on solder lugs at the top and bottom of the pvc former. Calculated and measured values gave an inductance of around 300mH. As with all plate chokes, check for self resonances with a GDO. I found some above 30Mhz but none were apparent between 160m and 10m. Self resonance can cause hot spots, and in severe cases, the choke will burst into flames. If you do find a resonance near to an amateur band try to eliminate it by winding on more turns or taking some turns off. The high tension can be connected to the plate choke via RG213 coaxial cable. Strip off the PVC jacket and remove the braid to leave only the inner conductor and polyethylene insulation [ rated at 5kVrms ].

RFC 1 and RFC 2 are parasitic chokes designed to suppress VHF oscillations. I used 6 turns of 1.5mm enamelled wire close wound with a diameter of 6mm. The chokes were terminated on the plate connectors, and their common ends were connected to the plate choke via a short length of tinned copper braid removed from miniature coax cable.

The 0.001mF RF bypass capacitors at the filament pins as well as at the screen grids are all 3kV ceramic types which can handle RF current. Twenty or thirty years ago you would find mica capacitors specified for high RF current applications, however while they are still being manufactured, they are not readily available in Australia. The plate DC blocking capacitor is made up of 2 x 2200pF ceramic capacitors in series. Each has a voltage rating of 6kV. In Brisbane, David Hall Electronics sells these - tel (07)3808 2777.

Band selection. | Optional ALC.
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