The system with the two controllers.
It looks like an old tape player,
and is same as the National Adversary from NS.
Heathkit's GD-1999 is a strange PONG system. Although Heathkit was famous for selling high
quality products, the GD-1999 was not a real kit. As a matter of fact, this system was a
clone of National Semiconductor's "Adversary" system (model 370, released after NS launched
the MM-57100 game chip in 1976). The system is same as the Adversary with one exception:
the label says "Heathkit GD-1999" instead of "Adversary", and the model passed from 370 to
GD-1999.
Another reason for not being a real kit is the electronic circuit board. Rather than being
hand soldered, it came fully assembled, adjusted and tested. Only a few solders were required
to wire the controllers to the circuit. The rest was really simple: screwing the two parts
of the case after putting the circuit inside. The user manual shows quite well the ease of
assembling: only four double-sided A4 pages instead of the thick 100-page manual full of
illustrations and details like of the GD-1380, which was a true kit.
Talking about the electronic circuit board provided by National Semiconductor, another
obscure system (supposedly a kit) was made by GEMINI (model 7640) and used the same circuit.
If the Gemini 7640 was released in late 1976, the GD-1999 was released in 1977 and sold at
a very low price. Curiously, not many sold (maybe a few thousands or less: the pictured
system is one of the first 800 produced).