22-11-2018, 12:09 PM
The surge in a heater chain is limited by the resistance of the chain. So for Trevor's eaxmple it would be 235/90 = 2.6A. Hardly damaging, as it will be going on for less than 10ms as the cap charges. This is also much less than the thermal time constant of the heaters. This is a different surge to the one caused by the low cold resistance of the heaters. That will go on for signifcant fraction of a second.
The capacitor is a good KISS solution. Easy, simple, cheap.
You can't use a cap dropper for HT, for example to replace resistive line cord. You might just about get away with it on a "cut and try basis" but the peak pulse currents taken by a halfwave rectifier make it very hard to predict what will actually happen. I suppose that if the heater chain current is a lot greater than the HT then you'd get away with a single dropper cap for everything but that's unlikely to happen in practice.
The capacitor is a good KISS solution. Easy, simple, cheap.
You can't use a cap dropper for HT, for example to replace resistive line cord. You might just about get away with it on a "cut and try basis" but the peak pulse currents taken by a halfwave rectifier make it very hard to predict what will actually happen. I suppose that if the heater chain current is a lot greater than the HT then you'd get away with a single dropper cap for everything but that's unlikely to happen in practice.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
