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Vintage Radio

Manufactured just before World War 2, the STC 504 is a 5-valve table receiver housed in a very attractive timber cabinet. It's an interesting circuit that performs well, especially after a few minor tweaks to its AGC system.

By Rodney Champness, VK3UG

The very first radios used breadboard construction, then came the coffin style before the large consoles of the 1930s and 1940s became dominant.

During the 1930s, compact sets that could be placed on table tops were also developed, although they were still usually too large for a mantelpiece. Many of these sets used a tuning dial located on a sloping panel on the top of the cabinet, which meant that they had to sit on a table or low cupboard.

These days, it’s hard to envisage such sets sitting on a lounge-room table away from the wall where power, antenna and earth were available. However, many were positioned that way and became the focus of the family’s entertainment.

There is no doubt these table sets were much more attractive than the average mantel set. For a start, they were usually housed in good-quality veneered timber cabinets. And although their sound quality would have been inferior to the consoles with their well-baffled 300mm (12-inch) loudspeakers, they were considerably better than the mantel receivers.

This month, we take a look at a typical table radio from the era, the 1939 STC 504. It is a mains-powered 5-valve superhet design that covers the broadcast band only (ie, no shortwave).

The STC 504 5-valve receiver

The unit featured here is one that I have on loan and is quite an interesting set. It’s housed in a nicely-finished timber cabinet which measures 460mm long, 255mm high and 270mm deep. The complete set weighs 10kg, so it’s no lightweight.

Unfortunately, the set is no longer completely original. The chassis had been overhauled several years ago, while the cabinet had only recently been restored. This restoration work has not been completely successful though, as explained later.

An unusual feature of the set is the mounting arrangement used for its 200mm (8-inch) speaker. This is attached to a fairly thick baffle which is mounted at an angle across the front lefthand corner of the cabinet. This baffle is quite effective for such a “compact” cabinet and contributes to the set’s sound quality.

The dial-scale is rather elaborate in appearance and is mounted on the righthand side. As with many other dials of the era, it looks quite impressive when lit up at night.

The three controls are mounted underneath the dial escutcheon. From left to right, they are: Tone, Tuning and Volume.

A glance inside the back shows just how tightly packed the cabinet is, with the chassis occupying the remaining space next to the loudspeaker. Apparently, the cabinet didn’t have a back which was not uncommon in those days.

Click for larger image
Fig.1: the circuit is a fairly typical superhet design employing five valves, a 450kHz (later 455kHz) IF stage and an electrodynamic loudspeaker. The sensitivity control is unusual and was difficult for the average user to master.

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