Like the dissection scene in the Quatermass film, Echorec restoration can be gruesome and genuinely terrifying work. As we worked our way deeper and deeper into the machine’s decaying innards, replacing wires and meticulously removing decades of crud the workbench gradually became littered with debris, desiccated fragments of cable insulation, the remnants of corroded wire. Even the wires from the power supply filter choke were rotten and corroded and there really was nothing to be done except bite the bullet and replace it. This is not a task to be taken lightly as the machine had to be stripped down—removing the side, top, bottom and front panels—just to gain access to the choke.
Binson N.O.S. (New Old Stock) chokes for the T7E aren’t readily available however, with some spade-work, an off-the-shelf ‘Hammond’ choke makes an excellent substitute. The Hammond fixed inductor 5H 75mA filter choke (Hammond part# 156L) is a close electrical match to the original part and is of similar physical dimensions. There’s just one proviso though: the pitch of the mounting holes, which are several millimeters too close together. This problem was solved by carefully machining the holes to turn them into slots—now the choke can be installed and soldered into the Echorec.