That is the oldest version, with three relays. This model puts the final tubes on standby in "Low" mode. Has a separate Tune and Load for Low side. The third relay, seen between the two sets of tubes directs the output of the driver tubes directly to the antenna for Low side and directs it into the cathodes of the final tubes for High side.
The third relay had breakdown problems. D&A changed both the Phantom and the Maverick to a two-relay setup. All the tubes remain in line for both High and Low. The power supply voltage is dropped in half for Low side. Much less complex to build, and one less chronic part failure in the design.
If the mileage in yours is low, that High/Low relay may serve you for a while to come. Might have a close-up look at it with a bright light and a magnifier, just the same. Look for cracks in the black plastic contact-insulator block.
73
