The V72 was developed at the NWDR (North West German Radio) between 1949 to 1952 as
a microphone and main studio amplifier under the technical supervision of Prof. Nestler, the former Head of R&D of TFK
ELA (Electro Acoustic) Lab.
Following the
Stockholme Radio conference, where Europe set the beginning of the Ultra Short Wave Radio or in better terms FM radio, new
equipment with a better frequency response and S/N ratio was needed. Because most pre-war equipment had been deported or destroyed
the NWDR developed a complete new standard for the German radio network in cooperation with the IRT in Hamburg (Institute
for Broadcast Technology). The V72 was modeled on the basis of the V41 (developed in 1928 by TFK), but with modern parts
like the Noval glass tubes and in a smaller housing: the "Danner" cassette module. The first 300 units were built
at the NWDR Zentraltechnik up to serial #100 and to Serial #300 by Maihak with a set of EF40 (the post war version of the
EF12). Later this tube was changed to a better version of the EF40, the EF804s.
The V72 is a self contained amplifier with a fixed gain. It was originally
used as a microphone amplifier (in use with a Neumann W75k high pass filter) and as a buffering amplifier to make up for loss
of the passive fader like the Danner MR66/88 and Eckmiller W86 EQs.
Up
to 1955 it was the standard preamplifier in German radio stations; with the introduction of the V76, it was pushed back as an input module, then only used as a buffering amplifier.
In 1963 it was decomissioned by the IRT and replaced by the V72t transistor version.
An estimated 25000 V72 were built for the German
Radio Network alone with a fixed gain of 34dB, by several different companies. The early ones were built by Maihak and TFK.
In 1954 Siemens and TAB joined the production team. Aside from the German radio stations, the V72 was used by most of
the European Recording Companies like EMI, Decca/TFK, etc. Those units were a bit different,with a fixed gain of 40 dB and
lower input impedence.
TFK used them as standard preamplifiers
for their broadcast division. In 1960 AEG-TFK, which was the world's biggest manufacturer of broadcast systems, sold these
units mainly to radio stations in South America, Africa and the Middle East, where most of them are still in use today. In
1966 the production stopped at TFK. Siemens stopped their production in 1964 but built the V72b version up to 1966.
TAB was the only company that built the V72a up into the 70s.
Today
the V72 is still in demand, but most units are now at least 35 years old and need to be rebuilt or refurbished. The electrolytic
caps of the power supply are dried out and need to be replaced; the silkwire of the unit falls apart, and in most cases it
shorts out the input/output x-former.
Technically
speaking, there is a family of V72 type amplifiers that were built around the V72 circuit: the V71, V77 and V78. The
close relatives to the V72 are those units that matched the technical data of this little giant, but used a different circuit
like the V72a (V74a) V72b (V70/V77b).
The
V71 was only made by Malotki and was a half size Danner module (without power supply) that incorporated the V72 circuit. The
gain could be set with a resistor from 19 to 43 dB and needed an external N52 power supply.
The V77 was a Siemens made supercharged V72 with a maximum gain of 80 dB.
It produced sound like a V72 but with the gain and plus of the V76. With an external switch (W77) the gain could be
adjusted from 0 to 80 dB. Tube set-up, choke and output x-former are identical. The input x-former is wound the
same way but with a 1 to 40 ratio, because in order to get the required S/N ratio the V77 needed a different power x-former
with two separate filament windings.
The V78 was a general purpose or talkback version for the German radio station with an adjustable
gain up to 70dB. Sound and S/N ratio is quite different, even where the circuit and transformers are the same, but the inputs
and outputs transformer are hooked up in a different way so that the unit loses its sound character. The V78 is quite easily
changed back to meet the V72 specifications.
The
V72a was the TAB follow up of the V72. The circuit is quite different, incorporating an EF95 and E180F pentodes, and
directly related to the V74(a). The sound of this mic pre was different but was a better following/buffering amp than
the V72 because it could take the higher output level of the V76. Some people call it the poor man's V72 because
it is easier to find than the V72. Both versions, V72/74, have problems mostly with the input x-former; they are either
blown or missing one leg.
The V72b was the
Siemens follow up of the V72, a symmetric/balanced mic pre
incorporating the E283CC and the E88CC. It was completely
different in design to
the V72 but soundwise on the same level, with better S/N ratio and intermodulation distortion.
It is a good mic-preamp but a much better mastering amp, directly related to the V70 and V77b. Like the V72a the V72b could also easily take the high output level of the
V76 with way more head room. Converted to the V77b, it is "The greatest mastering tubeamp of all times"...
As already mentioned, the original design of
the V72 goes back to 1928 with the V41. Closely examined, it is, except for the gain control, nearly the same amplifier.
After WWII Western Germany built the V41b (TFK/Maihak/EAB/Siemens) up to 1949 and replaced it with the V72, eastern Germany
built it until 1958 (Funkwerk Erfurt/C. Lorenz AG/RFT) and then replaced it with the V241. This version was more likely a mix between the old V41 and the western V72.
The tube setup was EF866 (made by the East German TFK) that is pretty much a EF806s and a ECC85. The gain control featured
the old V41-style circuit, 20/25/30/35/40/45/50 dB frequency compensated. The V241 was built by RFT, and in 1975 was replaced by the transistor version.
As well
as the V241, the V76 incorporated the V41 gain control, a feedback control, but TAB went one
step further and added a switchable input pad. The change resulted in a 12 position gain switch in six dB steps.
