Mantel receivers for use in the kitchen had become quite popular by the late 1940s, with both economy 4-valve units and more up-market 5-valve units being sold. However, as that market became saturated, manufacturers looked at adding extra features to keep buyers interested. Electric clocks had by then been around for some time, so the manufacturers hit on the idea of incorporating them into mantel receivers.
One result of this was that such sets could now also be used as bedside receivers, since they invariably included an alarm system. So instead of the user being awoken by an alarm clock, they could instead by roused by the radio automatically switching on.
In addition, the clock typically switched a mains socket on the back of the chassis. A bedside lamp could then be plugged into this socket, the idea being that the lamp would switch on at the same time as the radio.
Another common feature was the “sleep” or “slumber” mode. This typically allowed the user to leave the radio on but to set it so that it would automatically turn off up to an hour later. Of course, this all worked as long as the mains power didn’t go off during the night!
Fig.1: the circuit is a fairly conventional 5-valve superhet design, although the valve types differ from those generally used by other manufacturers.
The STC A5150 clock radio
STC’s A5150 clock radio was first produced in 1955. It is a typical 5-valve mantel/bedside receiver with an in-built Smiths electric clock. As an aside, it’s worth noting that most manufacturers built two versions of their mantel receivers during this period – one with a clock and a cheaper version without a clock. As far as I can determine, the receiver-only version of this unit was designated the A5140, which came out in 1954.
A feature of the A5150 is its unusual but interesting plastic cabinet. In fact, it looks like two cabinets grafted together!
The lefthand end of the cabinet carries a large rectangular dial scale, while the tuning gang is on the chassis immediately behind the dial. The tuning control is at the righthand end of the cabinet and this drives a long brass shaft which runs right across the chassis and through a bracket mounted on one end of the gang (see photo). This shaft then drives the dial drum and the dial pointer via a dial cord assembly.
It’s an unusual arrangement but is still very effective.
The loudspeaker is located immediately behind the dial. This was a fairly common arrangement in mantel receivers as it saved quite a bit of space. The loudspeaker has an oval-shaped frame and is a permanent magnet type with a 3Ω voice coil.