ON7UN Amateur Radio
 23cm HPA
Inside This Site
TH327 cavity mods
TH308 cavity mods
Amplifier  Housekeeping
PWR Measure



The High Power Amplifier used is a modified Plisch / Rohde & Schwarz TV transmitter's amplifier. The original amp is designed for 1 kW TV class A output in the 470 - 860 MHz frequency band. Modifications on the mechanics and electronics of this amplifier are necessary.

Expected gain of this amp is between 8 and 10 dB. The TH327 tube from Thomson has been designed for 14 dB gain, but we are using this valve beyond it's frequency specs, and the available tubes are 'pull's'. Most TV broadcasters change the tubes in their amps every X hours, these tubes are still very useful for us. Unfortunately not so many tube amplifiers are still in use for TV use in these power levels, most of the transmit stations went for solid state. ( of course, if it was not the case, we would not have been able to lay our hands on these surplus amplifiers )

Below are some pictures of the HPA mounted together with the driver amplifier. Below these pictures, the output power measured on the bird. ( read upper scale ! )




Webdesign Eddy ON7UN