|There are many features which can help to date a radio, including the types of valves (or transistors), type of circuitry, dial markings and even cabinet style. If you know where to look, an exact date of manufacture may often be found and for specific models their date of introduction will be available. Assuming one does not have specific information to hand however, the following details may prove useful.|
Valves may be categorised by their
type numbers and their bases. Sets in the UK, Europe and the
US tended to use different types of valve but, for simplicity,
I have concentrated on UK sets and main trends only:-
The all-glass B8A valve with a side
pip was used in later valve radios and followed on from IO types
in the period starting about 1947 and was probably favoured because
it didn't come loose, being held in place by a springy holder
gripping the glass pip. B7G and B9A types required a screening
can to hold them secure.
Transistors were initially germanium (Ge), and the more common types are characterised by a leading "A" or "O" in their nomenclature. Although it was invented in 1948, the transistor was very expensive and therefore only commonly used from about 1956/7. The first transistor set was the Regency TR1 made in the USA in 1955 and the first UK set was the PAM 510, made by Pye in 1956. Germanium transistors in RF stages usually required neutralising to combat positive feedback due to high interelectrode capacitance, and early transistor IF stages are prone to oscillation if incorrectly tuned or if components having different characteristics are substituted. The shape of a transistor will often indicate its original design date. Early types, not surprisingly, look old and may be "top hat" devices, made by GEC, or the fat four-lead Mullard types such as OC170.
The silicon transistor (Si) introduced in the 1960s, was basically immune to the undesirable temperature effects, such as thermal runaway and critical biasing characteristics of the Ge types but were much more expensive than their Ge counterparts. Germanium transistors were still used, for cost reasons therefore, up to about 1970. After a period when Ge spares were difficult to find, these seem to be once more available in limited types. Roberts used a combination of Ge and Si in that year (1970) but, for example, Grundig were still using Ge in 1975, nearly 20 years after their introduction. The manufacturers presumably chose the cheapest device available consistent with ease of manufacture; higher cost Si types for easy RF alignment and cheap Ge types for low cost audio stages.
Later the silicon transistor, its number
usually starting with a "B", at least in Europe, took
over universally when its price dropped, because it was a more
stable and resilient device, particularly being not as critical
to use in RF amplifiers. Early types have metal cans but the
more modern types have plastic cases. If you have a Japanese
transistor radio you will find its transistors are typically
marked C1302 or A1173 (the lower the number the older the transistor).
The markings are shortened from 2SC1302 and 2SA1173. The "2S"
is normally dropped and the leading letter "A" or "B"
means the device is a PNP and "C" or "D"
means NPN. The (missing) figure 2 represents the number of legs
less one. A 3SK104 would be a FET with 4 legs. Here, K is N-channel
(and J is P-channel). The "S" of course stands for
Silicon. American transistors often use "2N". Here
the lower the number the older the device but, unlike Japanese
coding, the code is totally anonymous and provides no clue as
to its type. Beware of small European transistors which sometimes
adopt a code such as "C107". This isn't "2SC107",
it really means "BC107" but there wasn't room on the
case to fit it all in and still be large enough to read! On that
topic "surface mount" transistors are the very devil
to identify as abbreviations are rarely unique (and sometimes
not even used).
Later sets used a dial calibrated in wavelength often with separate long and medium scales but had no station names.
For receivers with stations marked on its dial, take the latest date of the marked stations and subtract a year. For a handwritten list you may be able to use callsign information or wavelength.
Aberdeen (2BD), Nov 1922, 361m
Belfast (2BE), Sep 1924, 306m
Bournemouth (6BM), Oct 1923, 326m
Birmingham (5IT), Nov 1922, 384m
Cardiff (5WA), Feb 1923, 353m
Chelmsford (5XX), Jul 1924, 1600m
Chelmsford (5SW), Nov 1927, 255m
Daventry (5XX ex-Chelmsford), Jul 1925, 1554m
Daventry (5GB), Aug 21, 491m
Daventry National (5XX), Oct 1929, 1554
Droitwich, Oct 1934, 1554m
Dundee (2DE), Nov 1924, 294m
Forces Program, Jan 1940, 342m
Glasgow (5SC), Mar 1923, 405m
Home Service, Sept 1939, 394m...replaced National & Regional Programmes
Hull (6KH), Aug 1924, 294m
Leeds-Bradford (2LS), Jul 1924, 250m
Light Program, Jul 1945, 251m
Liverpool (6LV), Jun 1924, 297m
London (2LO), Nov 1922, 361m
London National, Mar 1930, 261m (Brookmans Park)
London Regional, Mar 1930, 356m (Brookmans Park)
Manchester (2ZY), Nov 1922, 384m
Midland Regional (5GB), Oct 1929, 479m
Newcastle (5NO), Dec 1922, 312m
North National, Jul 1931, 301m
North Regional, Jul 1931, 479m (Moorside Edge)
Nottingham (5NG), Sep 1924, 275m
Plymouth (5PY), Mar 1924, 350m
Scottish National, May 1932, 288m
Scottish Regional, May 1932, 376m
Sheffield (6FL), Nov 1923, 272m
Stoke on Trent (6ST), Nov 1924, 294m
Swansea (5SX), Dec 1924, 294m
Third Program, Sep 1946, 460m
West National, 1933, 256m (Washford Cross)
West Regional, 1933, 285m (Washford Cross)
Some loudspeakers have the date of manufacture on the back or side of the magnet housing although (if you are lucky because the speaker will be immaculate inside) you might have to untie a black cloth bag to see the details.
Some manufacturers use date stamps on the chassis or on a label fixed to the inside of the cabinet. Upend a radio (make sure there's nothing loose inside first) and see if there's a date on the underside of the cabinet. Look for codes ending in the last two digits of the year of manufacture. Repaired sets might have later dates on parts.
Mains powered sets started to become popular around 1929. By that date the country still had a mixture of AC and DC mains. Mains voltage was not standardised and varied from say 100 to 250. Some mains sets used a range of valves with higher than normal heater voltages, typically 20 and these were suitable, in series connection, for use with DC mains, however most early mains sets used a mains transformer which would be useless if you had a DC mains supply. The early mains valves had 4 volt heaters but these were gradually replaced by 6 volt types from about 1937. Some mains valves even had directly heated filaments which made them useful only in large signal circuits. A thing called a "humdinger" appeared for reducing hum and was basically an adjustable centre tape for grounding a directly heated AC filament. Battery powered sets were still in common use in the years before the war and it was common for bicycle shops to repair radios because that is where one took the filament accumulator to be charged.