RFT KM/T 70/50 1951

The KM/T 70/50 is documented as an East German RFT crystal microphone dating to 1951, making this an exceptionally early piece of post-war East German microphone production. Surviving examples are uncommon, and closely related KM/T 70/53 and KM/T 71/53 models followed a few years later. 

OPTICAL CONDITION

Very good vintage condition.

A beautiful surviving example with the unmistakable industrial appearance of early East German broadcast and communications equipment.

The construction is extraordinary by modern standards: the microphone is essentially entirely metal. Head, stem, mounting hardware and substantial cast base are all metallic, with virtually no plastic used anywhere in the microphone itself.

Normal signs of more than seven decades of age are present and have intentionally not been erased. The original RFT badge remains prominently displayed on the front.

Please examine the photographs carefully for the exact cosmetic condition.

TECHNICAL CONDITION

Restored / Modified — fully usable.

The original crystal transducer was tested but produces only an extremely faint output. This is not unusual for an early crystal element: the piezoelectric material and associated mechanical structure can deteriorate substantially over many decades.

Rather than presenting the microphone merely as a non-functional historical object, I decided to make this particular example usable again.

A modern dynamic microphone capsule has therefore been carefully installed inside the original head, and the microphone has been converted to a standard 3-pin XLR connection.

It can now be connected and used like a conventional modern dynamic microphone — no external polarization or phantom power is required.

Importantly, The original 1951 crystal capsule is supplied together with the microphone and remains part of its history.

AN EARLY MICROPHONE FROM THE DDR

The KM/T 70/50 belongs to the very beginning of the East German RFT era.

The model is documented as a crystal microphone from East Germany dating to 1951. That date places it only two years after the establishment of the German Democratic Republic.

the original KM/T 70/50 relied on a piezoelectric crystal transducer. Mechanical movement generated an electrical signal directly through the piezoelectric material, meaning that the microphone required neither an externally polarized condenser capsule nor an active amplifier.

It was an elegant solution for its period, but crystal elements have one significant disadvantage from today's perspective: they do not necessarily age well. Moisture, temperature, deterioration of the crystal material and changes in the mechanical coupling can leave a surviving microphone with dramatically reduced sensitivity.

That is precisely what happened to the original element in this specimen.

BUILD & DESIGN

The KM/T 70/50 is a wonderful example of an era in which even relatively straightforward microphone equipment could be built almost like machinery.

The circular microphone head is carried by a long, slender metal stem emerging from a large cast-metal tabletop base. There is effectively no decorative plastic shell disguising the structure — what you see is metal, weight and mechanical construction.

The proportions are particularly striking. The small circular head appears almost suspended above the massive base, giving the microphone an unmistakably early-1950s institutional and industrial character.

More than seventy years later, it remains a genuinely beautiful object.

ORIGINAL HISTORY — MODERN FUNCTION

This specimen deliberately occupies an interesting middle ground.

The historic RFT body, stand and construction have been preserved while a modern dynamic element gives the microphone a second working life.

The original crystal capsule accompanies it.

So the next owner receives both sides of the microphone:

the original 1951 component that tells its history — and a working microphone that can actually be plugged into an XLR cable and used today.