19-12-2020, 04:06 PM
I know that David and Trevor are very familiar with this, but others may not be so aware of the special problems faced by a boost/efficiency diode such as the PY81.
The cathode has very high voltage pulses, several kV, during flyback. Hence the cathode is the top cap. Thes diodes also need exceptional insulation between heater and cathode. A side effect of this is that it takes longer for the heat from heater to warm up the cathode. The boost diode is usually highest in the heater chain since it can easily withstand the voltage difference between heater and cathode.
Before specialist boost diodes such as the PY81 (also, later, PY800, PY801, PY88, PY500) were available, clever designers repurposed other diodes in different circuit configurations that reduced the pulse voltage on the cathode. For example PZ30 in the Bush TV22.
The cathode has very high voltage pulses, several kV, during flyback. Hence the cathode is the top cap. Thes diodes also need exceptional insulation between heater and cathode. A side effect of this is that it takes longer for the heat from heater to warm up the cathode. The boost diode is usually highest in the heater chain since it can easily withstand the voltage difference between heater and cathode.
Before specialist boost diodes such as the PY81 (also, later, PY800, PY801, PY88, PY500) were available, clever designers repurposed other diodes in different circuit configurations that reduced the pulse voltage on the cathode. For example PZ30 in the Bush TV22.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
