AN/UPX-4 a 23cm Amplifier with six 2C39As
The AN/UPX-4. This unit was actually made by OZ9CR, and although based upon the original UPX-4 unit, has been redesigned so that it will correctly tune and operate on the Amateur 23cm (1296MHz) band.
Tip - first download the construction drawings 
(664kb) and refer to these as you read this page.
Input and output tuning is via the adjusting screw mechanisms which can be seen protruding to the far left and right of the above picture. The N type connector at the bottom left is connected to a coupling probe which penetrates into the cathode input cavity. The anode cavity is slightly larger in diameter than the cathode cavity and three plastic tubes (only two in the picture) carry part of the air flow from the cathode cavity air supply to keep the anode cavity cool. The output N connector in the top middle of the photo goes to a coupling loop which protrudes into the anode cavity.
The holes in the cathode and anode cavities are the outlets for the exhaust cooling air. The brass wire meshes on the photo below are for the exhaust anode cooling air.
A view of the anode end showing the tuning rod, the inlet for the anode cooling air, the HT connector, and the rf input N connector (left) and the rf out N connector (right).
The cathode and heater connections for the six 2C39As. The cathode tuning mechanism can also be seen.
Another view with the anode tuning assembly (right) detached from the main amplifier unit (left)
A "boresight" view of the PTFE anode tuning rod in the centre of the right unit, and looking into the anode cavity (left). In the centre of the anode cavity is a rod protruding up from the bottom of the cavity. The PTFE tuning rod (which is actually a hollow tube) creates a dielectric tuner between the tube protruding from the top of anode cavity and the rod attached to the bottom, i.e. as the PTFE tube is inserted and retracted, the capacitance varies which tunes the anode cavity.
Although a PTFE rod is used for cathode cavity tuning, this is attached to a brass tuning plunger, so the cathode cavity is tuned a conventinal manner. i.e. the PTFE is not used as a dielectric tuner.
Another view of the two parts of the amplifier. The HT contacts the 2C39A anode plate via a spring which can be seen inside the anode tuning housing and a 7 o'clock position. The anode tuning housing also ducts the cooling air down and through the anode cooling fins of the 2C39As. A piece of insulating material inside the inner airduct ( the PTFE rod runs down the centre of this) contacts with the tops of the 2C39As so that the air has to go through the anode cooling fins.
With the 2C39As installed.
So you want to build your own UPX-4?
Download the AN/UPX-4 Construction drawings in (664kb)
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Page last updated 8/5/2001