I've been involved with Discovery Electronics and their products for a long time, and also with George Payne for a few years. Reg Sniff and I were the two people who tested every prototype and final version of the chips George Payne programmed for the Cointrax models, and I spoke with Alan Hughes, who was the marketing director at C-Scope then, several times re the CS-5ZX and 4ZX when they were first produced. Both of those models, and the CS-8SST which is a 5ZX with letters instead of coin designations for meter ID, use a George Payne designed, stand alone, simplified version of the Treasure Baron Cointrax module. I got a CS-5ZX right after they were released in 1997 or early 1998, and have one.now as well as three other Baron versions. The board in the the SST and 5ZX, also the 4ZX and 8SST according to Roy Van Epps at Discovery, are basically identical. They all have the three different audio option capability and notch circuitry but don't have the switches and jumper configuration on the boards to allow changing the audio or the potentiometers required to be able to use the notch. In addition, the sensitivity was restricted on those models but installing a jumper across the J-3 contacts on the circuit board removes the restriction and allows full sensitivity. The SST had the jumper installed at the factory, as well as the switch and jumper configuration to allow the three different audio options. The Cobra II and Viper were built by Discovery as house brands for Kellyco after Gold Mountain shut down, the current Cobra and Viper models they sell are built in China. Discovery made the Hothead coils for the big K for several years after Wilson stopped making them, and also made the coils Jimmy Sierra sold for Whites detectors for a long time.