TUBE BASED GEAR

Apart from some active Equalizers by Klangfilm, almost all models from the tube era were assigned a letter plus a two-digital number denoting their function, regardless of the actual manufacturer. This table provides a detailed overview of the tube amplifiers available in the Federal Republic of Germany (FRG) in the 1950's *. Here, I shall skip gear such as recording/playback amps for magnetic tape, power amps etc. and restrict myself to models suitable for modern outboard use of today:

V41 - microphone preamp, variable gain, design goes back to the 1930's
V72 - multi purpose amp, 34dB fixed gain, 16dBu max. o/p
V72a - dto, different circuitry (feedback structure, triode output), 22dBu max.
V72b - dto, fully symmetrical cirtuit (triode based)
V72s - 40dB gain, similar to V72, used by European recording companies such as EMI, Decca, Telefunken…
V74/a/b/c - buffer/line/splitting amp (usable as mic pre with high output mic's)
V75 - summing amp
V530 - dto, different circuitry
V76 - microphone preamp, gain control (76dB max), switchable hi/lo-cut **
V76s - special version with different filters and insert point for FB76 (see below)
V76m - different gain structure, no hi-/lo-cut filters, intended as measurement amp
V77 - max. 70dB gain, switchable externally with W77, similar circuit to V72
V77b - fully symmetrical & triode based (similar to V72b)
V78 - very similar circuit as in V72, higher gain (variable), originally used as talkback amp

FB76 - filter and limiter/compressor, for use as insert device with V76s
U23 - limiter (by Rohde & Schwarz)
U73/a - limiter w/ switcheable compressor, vari-mu design, fixed threshold & release
U73b - dto, controls for threshold & release
U74 - limiting amplifier (originally intended for talkback), unique combination of solid state amp stages with vari-mu gain control (similar to U73a/b) inbetween

RZ057 - Active EQ, high & low shelving plus mid band cut/boost with selectable HMF or LMF
RZ062a - dto, mid band has "tilt" EQ around 650Hz, similar to Eckmiller NF11 (see next section)
RZ062b - dto, mid band with presence boost only, four selectable frequencies
RZ086 - same parameters as 062b, uprated o/p amp stage
RZ088 - high / lowcut filter
The RZ modules actually consist of two passive EQ stages, each followed by a make-up amplifier.

* as for amp's used as micpre's today, note that the input impedance of V72, V72a, V76 and V77 is 2KΩ, 4KΩ, 600Ω and 400Ω respectively, thus varying up to a factor of 10. With the latter two resulting from high step-up ratios of the input transformers in order to provide enough gain, they can load down a mic output; as a consequence, the frequency response (as opposed to the nominal 1KΩ) may be altered, and (in case of condenser mic's), headroom may be compromised.

**although the V76 is hailed as the "holy grail" of German tube mic pre's, it is interesting to know that the HF / LF frequency response actually varies considerably depending on the gain setting, as can be seen here and here.


All V and U models are pentode based regarding amplification circuits (except where noted), have transformer balanced i/p & o/p and are self-contained with internal PSU, for ease of design regarding flexible size of consoles or other installations. The RZ modules need a dedicated power supply for anode and filament. All modules are relatively small in size (ecxcept for x23 and x41 models belonging to an earlier generation). They almost exclusively use the DIN41622 12-pin connector as a standard (mating connector e.g. here). Having been designed for a mains voltage of 220V, todays standard of 230V is actually a bit high, since it directly translates to the heater voltage being 5% higher than normal, shortening the life expectancy of the tubes. To counteract this, a VariAC (autotransformer with multiple taps) should be used to get the mains supply down to 220V.

Some of these modules still show up on the used market occasionally, others have become very rare. Subsequently, the prices went up considerably - while in 2005, you might have been able to score a V76 for 600 Euro, prices have tripled as of ten years later.
The 7x / RZ range originated from West Germany (FRG) being developed by the NWDR , produced mainly by companies such as Siemens, TAB or Maihak, and Klangfilm respectively.


Meanwhile, in East Germany (GDR), RFZ developed the "V200" range and had companies like Lorenz or Sander & Janzen build them. The concept was similar to the V72 approach, but most of these modules show up on the market very rarely. The only ones usable for outboard that I've come across so far are:

V213 - limiter, similar to U73, gain control uses feedback instead of feed forward topology
ÜV18 - East German designation for the original V41a micpre, steel tubes, max. 60dB gain
ÜV268 - dto, slight circuit variation (V41d)
V241 - later version of the above, glass tubes, dimensions similar to V76
ÜV300 - dto., alternate designation (possibly slight circuit variation, too)
V240 - line amp, useable as mic pre (max. 36dB gain)
V242 - line / buffer amp, symmetrical triode circuit