Radio construction methods evolved over the years, and as a result, specific styles of construction can be used to date antique radios to within a few years. Prior to 1920, radios resembled a scientific apparatus, which they truly were -- not the type we think of today. About 1920, the breadboard type of construction was popular. A large rectangular board was used as the base of the receiver, and the components were mounted on top. These were more similar to large radio kits that we see for kids today. Point-to-point wiring was found on the underside of the breadboard. Three sets of tuning components were provided; one for each RF circuit. Ganging controls had not yet been invented.
Like breadboard radios, many of the early table models used two or three separate tuning controls. By the end of the 1920s, however, the "three dialers" were disappearing and more modem forms of radio with a single control and window dial were coming on the scene. Many of these radios used an external speaker in the form of a horn.
Probably the one radio design that is truly representative of radios in the early period is the Cathedral model
This is what most of us think of when we think antique radios. These models were also known as the Gothic or upright radio. The cathedral radio was typically 18 to 22 inches tall, and had a base between 12 and 16 inches square. Tuning was generally of the one-knob type and the speaker was integral to the radio cabinet. These radios were made from the late 1920s until the early 1930s. This is generally the period of time from which one searches for antique radios, because prior to this period they were really not much to look at and certainly had no aesthetic value to add to a home.
In Britain, radio manufacturers were producing their own radio designs in parallel with the Americans. What the Tombstone and Cathedral models were to American purchasers, the "round models" were to the British user. Companies like Eddystone and Pye made radios in Britain paralleling American developments, and in some ways exceeding them.
Also becoming popular in the late 1930s and 1940s were the "modem" console, or floor model radios. Large consoles were made in the 1920s, but were extremely expensive, and limited to a more affluent market. But more mass-market consoles began to appear in the late 1930s, and the radio became an everyday piece of furniture.
All antique radios were based on the "vacuum tube"
If the radio does not have vacuum tubes in it, it can be considered "old" at best and virtually worthless! Vacuum tubes were manufactured from the first decade of the twentieth century, but did not become firmly established as a viable industry until after World War I. Even then, vacuum tubes were terribly expensive -- the cheapest of them cost a week's salary. It is rumored that McIvor Parker (W4II), who was involved in radio from the mid-1920s, once saved for months to buy three vacuum tubes at $7.50 each, in order to build a radio receiver. The tube complement of a radio receiver is often used to establish the approximate date of manufacture of the set. One of the best guides to this is laid out in The Radio Collector's Directory and Price Guide which contains a chart of tubes and their dates.
Because antique radios are based on and will have vacuum tubes, it can be a real challenge to restore an old broken one to a functional status. First, vacuum tubes are NOT easy to come by, expensive and have to ordered from a very limited set of suppliers. Second, tuning these old radios is tricky and requires a specialized knowledge set died out many years ago -- however, there are still a few radio techs around fully capable of helping with the restoration.
The good news that, for many, a working antique radio is not really that important and the primary concern is not a financial one. They are classic in their appearance and make a great furniture addition to any home where antiques fit in with the decor.
If you are looking for more information, we would like to suggest some of these areas on the web. DMOZ (one of the oldest and largest directories on the Internet) has a category dedicated to antique radios here. If you are lucky enough to have found an old radio that you need restoration help with, you might start your research at OldRadioDoc.com. This is a nifty site with some great example of antique radios and they actually provide restorations services. However, you may be a bit shocked when you find out how much restoration costs!