Ramsey Electronics FX Series Manual page 117

Stage TX: Transmitter Buffer, Driver and Final
The transmitter section, Q10, Q9 and Q8, is conventional VHF RF circuitry
that has proven quite reliable in Ramsey transceivers. Just a few circuit notes
are in order.
Transistor Q10, the transmit Buffer, amplifies the VCO output from C56 to
about 10 milliwatts, quite sufficient for checking modulation and PLL alignment
in transmit mode as soon as this stage is built. Operating bias is supplied by
the PLL lock detect voltage from U5B through R110. If the PLL unlocks, Q10
does not operate, preventing the radiation of out-of-band signals.
The 2N3866 Driver, Q9, amplifies the output of Q10 to drive Q8 to its full rated
output. Q8, the popular MRF237 or its equivalent, has physical characteristics
that the builder should understand. Many RF transistors of this style have the
Collector lead common to the case. Through sophisticated insulating
technology, the Emitter lead is common to the case. There is significantly
better gain because there is no emitter lead length to speak of. This relatively
small transistor package can handle large power dissipation IF the case is
properly soldered to the groundplane of the PC board as detailed in the
assembly instructions.The transistor is fully intended by the manufacturer to
be heat-sunk in this manner: don't worry about soldering heat damaging the
device.
An unusual part is C75, a SMT "chip capacitor". It is installed on the solder
side of the board, and its leadless design is what allows Q9 to deliver such
exceptional gain.
DO NOT install any transmitter parts without at least reading over the
assembly details first and the reasons for the sequence that we have
recommended. The PIN T-R diodes D7, D6 and D2 are discussed in section
DR. In brief review, D7 passes RF to J3 during transmit while D2 and D6
protect the receiver RF input. The antenna input is designed for a 50 ohm
resonant antenna. C84 and C74 are tuned for maximum RF output (3 to 5
watts). These adjustments are part of final transmitter alignment.
Maximum RF output depends critically on following the coil winding
instructions EXACTLY in Stage "TC".
Stage TX: TRANSMITTER SECTION ASSEMBLY:
Install the components in the order recommended and DO NOT under any
circumstances connect DC power to the unit unless instructed to do so at a
particular point. The following assembly steps presume that Stage "TC" (RF
coil and choke preparation) was done. Refer to "TC" if you have any question
on these parts, which also may be built up as you proceed.