Description of a 144 MHz HPA with 2 x 4CX250B tetrodes
LA0BY, last updated 18.12.2002
View of anode circuit ------>
This page provides information on the design and practical implementation of a rather inexpensive 144 MHz high power amplifier using a pair of ceramic tetrodes, type 4CX250B, in a push-pull configuration. I have used it mainly for MS and EME operation for many years. Important design features and measured operating parameters are displayed in the amplifier manual (26 kB PDF). The schematic diagrams (PDF 60 kB) and the following pictures reveal further details.
Pictures of power supply unit
Front, rear and top (open chassis) view
Close up of HV circuit
Close up of grid/screen supply
Pictures of RF unit
Front and rear view
Close up of output circuit
Close up of valve sockets and neutralising capacitors
Close up of grid circuit
There is also a set of construction drawings (PDF 91 kB) made by OM1CW. This amplifier has been rebuilt by many amateurs, among them also DL5DBM, DL6YEH, VK3OF. You may contact them for further details.