A decade or so ago, I played with some nickel cored versions of the Tannoy crossover parts for Arthur Loesch. Recently, Chris from Jupiter Condenser had me do a complete set using his 0.99999 pure cotton served copper wire.
The cotton serving takes up a fair bit of the winding space compared to typical magnet wire insulation so some creative license was needed to keep the parameters identical to the original. Luckily, the higher perm of the 80% nickel cores made this easy!
In the original design the ~0.5mhy inductor was air cored and had a rather high DCR and was in series with a ~4Ω resistor and I needed to juggle the DCR and and resistor values to net the same end result.
Since the theme here was 80% nickel, it only seemed appropriate to use that to my advantage for the above choke and sneak a few lams into the typically air cored inductor above to keep the family character.
Just finished up a LCR tape EQ for a customer in Hong Kong.
Single ended input and output with 40dB of gain and three different EQ filter options. (NAB, 7.5ips IEC and 15ips IEC) This follows the basic topology of our phono with permalloy output transformers and power supply chokes.
In this instance the customer needed a balanced input so I built an active Balanced to SE gain stage based on a pair of 2SK170's loaded with an 80% nickel transformer that brings the overall tape gain up to 60dB.