The sequencer protects those expensive RF relays from damage. What it actually does is operate the relays in order, allowing the contacts enough time to close and be ready for all that RF coming their way. It happens like this:
Key down, the antenna relays switch, 100ms later the cutoff relay turns on the tube, 100ms later the transverter is keyed. If you are not using a transverter, you need not use this last connection.
Key up, the transverter is unkeyed, 100ms later the cutoff relay cuts off the tube, 100ms later the antenna relays are released.
Caution should be taken not to operate the amplify/bypass switch while transmitting, as this will defeat the seqencing.
A simple analog switch/timer drives separate operational amplifiers, each switching at different levels on the charge/discharge cycle of the timing capacitor. The op-amps drive the relay driver transistors. If you wanted to include a remotely mounted preamp in the switching sequence, you need only to drive it's relay with the appropriate driver circuit controlled by the bottom op-amp. This will cause the preamp to switch out first, and return last in the sequence.