INTRODUCTION
The construction taken from the application report NCO8101 two amplifiers for band 4/5 with BLV57 transistors have been described. Reactions on this report proved the necessity to give more information about the construction of these amplifiers. This construction has been based on a heatsink with a printed-circuit board at the upper side and the bias circuits and a forced air-cooling at the lower side. (download datasheet for schematic and instruction).
PRINTED CIRCUIT BOARD
In the printed-circuit board rectangular holes have been made to mount the BLV57 transistors on the heatsink. For fastening of the printed-circuit board on the heatsink by means of screws, 7 holes of 3.1 mm Æ and for fastening of the hybrid couplers 8 holes of 2.6 mm Æ have been made on the indicated places (see Figs 1 and 2). Hereby has been taken into account the use of Anaren hybrid couplers, type 10264 - 3, suited for the frequency range of 500 - 1000 MHz. Because the 2 bias units have been situated at the lower side of the heatsink, the connections from these units to the circuit take place through the printed-circuit board and the heatsink. For this purpose 9 holes of 2 mm Æ are necessary (4 collectors, 4 bases and 1 ground). To make a good ground contact between the upper and the lower side of the printed-circuit board the following measures have been taken:
- On 8 spots rivets have been used and soldered at both sides to the metallization of the printed-circuit board. The holes of 2 mm Æ , needed for these rivets, have been situated as indicated in Figs1 and 2.
- Copper straps with a thickness of 0.2 mm have been soldered at all edges of the printed-circuit board.
- A good emitter to ground contact has been achieved by soldering 8 copper straps from the upper to the lower side of the printed-circuit board on the spots of each emitter lead.
- The input connector and the output connector have been screwed to the heatsink but the ground also has been soldered to the printed-circuit board.
HEATSINK For the BLV57 amplifiers, described in report NCO8101, a blackened heatsink of Seifert Electronic, type KL-117 with a length of 191 mm has been used (see Fig.3). At the lower side forced air-cooling has been applied with a fan trade mark Etri, type 99 XU 01 - 81 with an air displacement of 16 litres per second). By applying this air-cooling the thermal resistance decreased from 0.5 °C/W to 0.2 °C/W.
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