QBL 5/3500 VHF amplifier

mechanical and design details


Mechanical details

The PA is housed in a box with the following dimensions : heigth 320 mm, width 300 mm, depth 340 mm.

The box is made of aluminum plate of 1.5 mm thickness. The plate holding the QBL 5/3500 divides the box in an anode compartment and a cathode compartment. The dimensions of these compartments are approximately :

Anode compartment 250*300*340    Cathode compartment 70*300*340  (thickness of middle plate not taken into account)

A list of materials can be found here.

The tube is used in the "anode-up" position. Various datasheets were used to gather tube data. Some explicitly stated an "anode down" use of the tube while others state "to be used in vertical position only". No averse effects have been encountered so far using the tube "anode up".

A special word of thanks to Jos, PA3ACJ. 

Jos provided a tremendous amount of help with the design and making of "difficult" mechanical parts using his lathe.


Electrical details

The amplifier is based on the original design of K1AGB, using a 3CX1500-A7 (8877). This design was described in QST of December 1973 and January 1974. The strip line is recalculated for a different height above the ground plane, due to the mechanical properties of the QBL 5/3500 tube. 

The electrical design is explained in this page. 



Given the high voltages used special attention has been given to the testing of the various parts.


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