The earliest known concept of putting two or more identical units inside a glass envelope goes back to the manufacture of the first double-filament De Forest Audions. Over the years several multiple or integrated valves were developed in the USA and England. It was in Germany that the idea was developed further. In the early twenties, just after WW I,
Fig. 278 - The Loewe valve type 3NF

Germany was under the restriction of the Versailles Treaty. Its bad economical situation had forced the government to levy heavy taxes on many products including, of course, radio receivers. The tax was determined generally by the number of valves used in the radio. Dr. Sigmund Loewe,
Fig. 277 - the electrical circuit inside and outside the 3NF valve.

founder and owner of the company Loewe Radio AG of Berlin, considered this peculiar situation and in 1926 working together with Dr. Manfred von Ardenne, the pioneer in the researches on the cathode ray tube, developed a thermionic device provided with several elements inside a single glass envelop which can be considered similar to a modern integrate circuit. Thus in 1926, the company lauched in the German market the first multipel valve. Later on, circa 1929, the Company developed an interesting small radio receiver that used as its circuitry a single multiple valve. Fig. 275
Considering the technology and materials available in the early twenties, the manufcature of such valve was not an easy task, requiring great proficiency in glass blowing as well as skill in assembly. Fig 276
The best known Loewe multiple valves are the original types 3NF and 2HF. The 3NF (nieder frequenz) was used for low frequency applications. I had a 6-pin bae with the following basic operation conditions: filament 4V a 0.3 A, anode voltage 135 V. This valve contained in a glass envelope three cascaded triode amplifier valves, with their anode and grid resistors plus the coupling capacitors. Fig 277
To avoid contamination of the vacuum in the envelope, the capacitors and resistors were sealed individually in glass capsules. Finally, the whole system was assembled in a complex metal-glass structure on a special base. Fig 278
Fig.275 - The O.E.-333 one-valve radio and its plug-in coils.

Similar in size of its glass bulb, and using the same 6-pin base, was the type 2HF (hoch frequenz), or a valve for high frequency applications. It consisted of two of two tetrodes arranged as a two stage RF amplifier with the following basic operation conditions: filament 4 V at 0.17 A, anode voltage 15 V.
In mid-'30s, the company product line comprised several types of multiple valves for AC operation, such as the types WG 36 using a metal-shielded envelope.
Due its peculiar concept in its time, the Loewe multiple valve was a step ahead as an innovative and reliable thermionic device whose production was never attempted elsewhere. Through his researche in circuitry, materials, and manufacturing process, Dr. Loewe started a new trend in electronics - the miniaturization of passive and active components - i.e., the birth of microelectronics - and in this way he can be considered as a forerunner .

Fig.278a - The multiple valve with 6 pins socket.
Fig.276 - the inner elements of the 3 NF valve.
Fig.277 a - X-ray view of the 3NF valve. The three triodes, two horizontal and one vertical, can be seen easily. Often they are not visible through the bulb due to the getter flash.
Fig. 278c - The American valve type 6N7. A twin triode made circa 1930 that can be considered also a multiple valve.
Fig. 278 b- the multipe valve 3NF complete.