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Abstract: A highly linear and high power PA can be constructed with the Siemens YL-1050 TV-Tube. The design evolved from previous work done by K2RIW with his Stripline-PA with 2x 4CX250 and a similar construction by DB6NT with a a single RS1064 tube. The YL-1050 has plenty of plate dissipation (1.6kW) and loafs along with low temperature even with lk+ outputs. Gain with this power level is 16 dB.
1. Design Approach
For trouble-free and cool operation for high duty application on 70 cm, i.e. moonbounce or MS-operation, this amplifier uses a YL-1050 tetrode in a cathode driven circuit. Grid 1 and screen grid are on RF-Ground. To simplify construction and reduce feedback the screen grid is on DC-ground also. Cathode and anode circuit are made from half wavelength striplines for easy tuning and loading. The YL-1050 tube has 1.6 kW plate dissipation and full ratings up to 790 MHz. Because of the large anode radiator cooling requirements are 1.2 mBar pressure with 1.5 m3 per minute.
2. Construction
Fi
Fig 2
Two boxes made from 2 mm aluminia compromise the plate circuit and the cathode circuit. The Anode circuit Box is shown in Figure 3.
Fig 3
2.1 Plate circuit
The plate circuit is a half-wavelength stripfine made from a 120x227.5 mm glass-epoxy PCB-Material, which 2 mm thick. The corners are rounded to minimize electrical field strength. The stripline is located on 42 mm long PTFE-Standoffs (Don't use ceramic standoffs, unless you are sure about their dielectric losses. Otherwise they will just explode with some 40 kW of RF-Power circulating in the anode box with a loaded Q of 40! The best test instrument for this purpose is a microwave oven for kitchens.). Tuning is done with flapper condensator Cl, which dimensions are 85x55 mm and is made from beryllium copper. Capacitor C2 is for loading and made from the same materiaL It's dimensions you can see from Figure 4. A ceramic standoff prevents rotation. The load flapper is soldered to the 7/16 Spinner ouput connector. N-Connector is not recommended for this, because the PA can easily melt the small pin of a N-Connector with full 'juice'. Both Cl and C2 are positioned by 6 mm PTFE-roda and excentric parts, which move these rods (Figure 4). That's much more stable than Lhe fishing lines used in other PA's.
Fig 4
Part 1 - Part 2.
OZ9ZI, Steen Gruby.