Even with the historical blueprints of most V series x-former, it was quite a challenge to recreate these very unique x-former. Most suppliers of the parts and material didn't exist anymore, and the ones that were still in business didn't even heard about their 50-year-old part numbers. By luck we recovered most of the original dies for the lamination, we found a specialty metal manufacture that agreed to make us 200kg of the need NI/FE/CO alloy. So the biggest problem was resolved, but even than we had to take care of all the other 64 little parts and pieces that were needed to make just one input transformer of the V72.

Three volumes of Telefunken ELA transformer blueprints rescued from a paper shredder when AEG-Telefunken closed their ELA division in the early 1990

It took us several days to build just one bobbin, plus sub bobbins (the V72 input contains six, the V76 8 and the V77 10 tiny wire disks), so we decided to build special tooling to make our production easier. After different tries we finally came up with several cuting and stamping machines to make all needed parts in a timely manner. Most basic components are still the same like they were used 50 years ago, hard paper, shellac and silk; during the time the V72 were introduced, phantom power wasn't required; with historic 500V insulation voltage, phantom power can be a problem. Most vintage V7x input x-former die slowly every time +48V is applied. Thanks to space age materials, like Teflon and UV activated plastics we could improve the insulation voltage to 5kV without compromising the sound. The new input x-former (some of them have a step up ratio of 1 to 40) handle phantom power without a problem.

The first few x-former were wound with the historic winding machines that were also used at Telefunken ELA division in Hanover, but due to tolerances of more than 10% we decided to invest into several high tech digital winding machines. Those machines are capable to wind with tolerances of less than 3%, a more civilized standard for matched dual channel mic pres like the new V72S.

Four Swiss made Meteor M20 and one M40 take care of all crucial steps to wind the audio transformer and chokes

The three-chamber plate inductor is mainly responsible for the high dynamic range of the V72 and V76, also the one that gave us a big head ache. Instead of a plain old resistor, a high nickel content inductor is used for inter- and output stage. About 6000 feet of magnet wire that is roughly 1/4 of the size of a human hair, wound with approx. 30000 turns onto a three chamber bobbin, keeping stray capacitance as low as possible. We found a bobbin manufacture that still had some NOS stock, but after getting the first samples, 40 years on a back shelf in a wear house made them same as fragile than the ones you find in the historic V units. Just careful touching can result in cracks or breaking. New ones couldn't be made, because tooling was decommissioned in the later 1970s. After several tries to replace it with Ferrite inductors, etc. we made a new set of tools.

So what is so special of this design? Not very often used in audio circuits, the only other application that we could find out was audio equipment made for the US Navy in the 1940s. The inductor allows a very high amplification over a wide frequency range with hardly any random noise created by standard plate resistor. Effective AC plate resistance is nearly 1M Ohm with a fraction of DC resistance, aside higher dynamic range, better S/N noise, it also allows less intermodulation distortion that gives the V72 and V76 its classic wide open tonal response.

Aside manufacturing new x-former, we also rewind most other historic audio transformer and chokes. We offer a wide range of replacement x-former for most vintage german studio equipment. Two years ago we started to supply several other audio manufactures with transformers. In case you looking for transformer repair/rewinding, replacement of missing transformers for vintage Telefunken mics made by Neumann or AKG, or in need of custom work, just give us a call or send a mail.