tektronix: 570; High Gm tubes oscillating in Type 570

There is a tendency for some high Gm tubes being tested with the Type 570 Characteristic-Curve Tracer to oscillate despite the use of resistor patch cords and shielding with Belden braid.
Tektronix Field Engineer Earl Williams reports considerable sucess in suppressing these oscillation through the use of Ferramic cores installed on each bare-wire lead connecting pin jack to tube socket plug. Ferramic cores are the ferrite material beads that can be strung on wire to act as suppressors to high-frequency currents flowing in wire. Earl says that brief test did not show that use of beads could eliminate possible need for resistor patch cords, but he was able to display curves he had not seen to date.

Source: ServiceScope Oct 1959

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