GS35b 2cm Amplifier
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Geert PA3CSG once got a hand made drawing of this amplifier. RW1AW identified its origin as ex UV1AS, RX1AS. The input circuit is slightly modified, and the construction of the output circuit is changed a little. This design will run at very high efficiency (65%)!

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The dimensions of the box are 83 x 17 x 17 cm. Made of 3mm thick aluminium.

Grid plate is made out of 2mm brass.

The plate line is a 55mm dia. copper tube 53cm long, from bottom of cooler to top of line.

Plate tuning disk is 80mm diameter opposite a 100mm x 100mm plate with a layer of teflon or mica sheet fastened to it.

Loading disk is 80mm diameter opposite a 100mm x 100mm plate with a layer of teflon or mica sheet fastened to it.

Air barrier is 1.6mm epoxy PC board with all copper stripped off.

Input tuned circuit is 17cm long copper wire 2mm diameter. A 0.5-3pF capacitor is in series with the input, and C to ground is an air C about 20pF.


First assemble the fingerstock in the brass plate and in the kathode PCB making the tube socket. Solder input L to the cathode board. Mount cathode on brass plate. Make sure that the tube fits correctly in the socket.

Mount brass grid plate in the aluminium housing. It is about 12cm from the bottom.

Drill holes for the input C and BNC input connector.

Drill holes for feedthrough caps.

Complete anode line with insulation and plate C's. The connection from the line to the GS35 is a machined part, one end to fit the plate line, the other end machined down to fit the GS35. The nut holding the GS35 cooler is removed and the plate line is used instead. Use a PTFE standoff at the end.

Push tube with plate line in socket and the air barrier and mark places where load, tune C and HT feedthrough have to be drilled. HT feedthrough is about 31cm from box end. Mark place where air barrier plate has to be mounted.

Take tube out, mount air barrier and drill holes. Mount tuning and loading C's and HT feedthrough.

Put tube with plate line back in and fasten it to the Bottom using a self tapping screw.

Finish input circuit soldering input series C to C to ground and to BNC connector. Mount cathode RFC's (2W 47K resisitor fully wound with 0.8mm enameled copper wire). Solder plate RFC (lambda/4 wire and cpacitor to ground 1nF)

Put end and bottom plates in. Place cover with blower on top.

For operational data, check the GS-35b table for 2m!
Click HERE to go to Geert's web site!

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