This is the Contex model 6706 amplifier. This particular model was marketed by more than one company, having ABC, Apollo, and Echo names as well as Contex stenciled on the front panel. This functionally simple amplifier featured twin rocker switches for power on and standby, Plate Tune and Antenna Load controls, plus indicator bulbs to show power on and relative R.F. power out (You tuned it for maximum brightness of the bulb). This was a basic 2 sweep tube (6JG6) single stage amplifier, capable of about 100 - 120 watts of peak power, and typically around 50 - 60 watts dead key with a 3 - 4 watt AM dead key. R.F. sensing was accomplished by a single 6BQ5 tube. There was no delay for SSB, so you had to keep some amount of background audio to keep it keyed or the relay would chatter.
Changing the tubes to more powerful types (6LQ6) could net a bit more peak power output, and was a common modification, although using the longer tubes did not allow the cover to be put back on. One trouble spot for this amplifier though, was a tendency to smoke the R.F. plate choke when the tubes started going soft. Fortunately this was a stock part (10 uH) at Radio Shack, and I always had a few spares on tap.
This was my very first amplifier, having obtained it in the late 1975 timeframe, as the result of a trade for the bicycle mobile. This amp mated well with my Lafayette Comstat 25, and later the Midland 13-885 I worked my first DX contact thanks to the extra kick that this amp gave me. The circuit for this amp was so simple (a basic grounded grid design) that I copied it and built a few amplifiers of my own over the years using spare parts and old television chassis power transformers.
I ended up trading this amp about a year later, along with my SBE Cortez, for a Tram XL-5.