SM6FHZ 432 MHz EME Power Amplifier

The power amplifier is a GS23b tetrode in a Russian TV Tx-cavity.

Operating conditions:

Ua: 3000 V
Ug2: 500 V
Ia0: 100 mA
Ia: 600 mA
Ig1: ~1 mA
Ig2: ~2 mA
Pin: 22 W

The front panel of the 70 cm PA during construction.

70 cm PA interior

The interior of the 70 cm PA during construction.

GS23b 70 cm PA

The 3 phase high voltage power supply, 3000 V, >2 A:

3 phase power supply

Parts of the cavity before and during examination and rebuilding for 70 cm operation:

Anode decoupling  Anode cavity  Input connector  Output end
Anode decoupling                                        Anode cavity                            Input connector                                        Output coupling adjustment axis

The cavity originates from a TV transmitter in Murmansk, I was told by Dr. Alex, UR4LL. It was brought to Weinheim where I should pick it up on the behalf of SM4IVE, Lars. I met with UR5LX, Sergej and UR4LL, Dr. Alex during the UKW Tagung in Weinheim in September 1994.

We all sat together in the big van of Rainer, DF6NA, chatting and drinking Ukrainian vodka together with DL9KR, Jan, SM6CMU, Ingo, SM6KJX, Jan, and others. I got the cavity and transported it to Sweden in the car of SM6CMU, Ingo.

The happy hams from Ukraine and Sweden in Weinheim, Germany in September 1994:

Happy hams in Weinheim
From left to right: UR5LX, Sergej (RB5LGX at that time), UR4LL, Dr Alex and SM6FHZ, Ingolf. The box in the middle is a 2 m PA from Ukraine.

SM4IVE together with SM4DHN made later modifications to the cavity in order to make it work on 23 cm, without success.
The cavity was sold to Hans, SM6EUP, in 1997, but Hans never put it into operation.
In the summer of 2006 I dragged the cavity from Hans shelf to my work bench in order to get it running on 70 cm. By the end of the year I had a kW out of it with good gain and efficiency. In order to get there I had to do a few modifications; the input coupling probe, the output coupling disk and more. To my help, I got good advice from Sergej, Dr. Alex, late Josep (EA3DXU), Paul (WA6PY) and others as well as from the WEB-page of PA0V.

Other UHF-HAM's known to use this same type of cavity are PA0V, Nanko, PC5M, Carel and GW8IZR, Paul.

So now
finally this cavity is back to daddy, where it belongs, after a long journey. I promise to use it as much as I can, to work you all on 432 MHz EME, for a looong time to come.

Updated August 22, 2009.