Mc Transistor Converter

The new Texas Instrument TIXMOo transistors were rated for operation at 200 mc but are surprisingly good at 432 mc. These units compare very favorably with transistors costing many times as much, and at about 50 cents apiece, a few extra can be bought in order to get some very choice ones for the front end of a 432 mc converter* The writer found that about one out of every three were red hot for 432 mc operation and the other two out of three were still better than other $3.00 types generally used at 432 mc. The only problem in their use is mechanical breakage of these plastic cased units. This can be minimized by using (lie new transistor sockets made for type TO-18 cased transistors since the three leads do not have to be spread out as when using Hie larger ( 10-5 type) sockets. The writer managed to break a few transistors in the first converter built here so a new one, shown in the photographs, was built with the new smaller sockets. No more breakage was encountered but it is a little upsetting to pay as much for a socket as for a transistor. Direct soldering of the transistors into the circuit might be an alternative but makes it hard to select die lower XT transistor for the first rf stage. This arrangement was used finally in the first converter in place of the large sockets though one transistor was damaged in the process of soldering* The small but expensive sockets are really the best solution.

432 mc antenna filter

In Fig. 1, a dual circuit antenna filter is shown which was built into an aluminum chassis box 12 x 211 \ 2!i inches in size. T^iis unit works reasonably well for receiving and for transmitting at low power perhaps up to 50 watts output. With a pair of 4CX250R tubes in the final amplifier, the aluminum box gets hot at the low impedance ends and circuits go out of resonance. The circuits would stay in resonance for a minute or so with 100 to 500 watts of rf power then the box gets w arm to the touch and losses go up as the circuits go out of resonance and dielectric losses also increase. Then end result was retirement of this antenna filter to the receiver iront end only since its losses, when cold, are approximately one db. The signal loss then is not too objectionable for normal 432 mc signal recep-

TAP up 40ûu1 3m" from gmd end ítypicau

TAP up 40ûu1 3m" from gmd end ítypicau

copper plates h/z" wide * 6-1/2" lg, ttot ad with 1/2" ltp each end appro*. 1/2" gap ceramic insulator 1/5 dia I ru.

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