Quote:
Originally Posted by Reece
Use of capacitors for filament string voltage dropping does result in a very soft start. I have seen about twenty seconds before voltage came from an initial approximately 60 up to just below line voltage on a string, so in such cases a CL90 wouldn't be needed. CL90's are good where you don't need to drop voltage (although they do drop a couple of volts) but want to just give a soft start. It's also a good idea to put a high value resistor across the dropper capacitors, around 100K, to quickly discharge them at shutdown. A quick turn off/turn on could send a surge through the string so a quick discharge helps.
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It seems like there are some really good ideas evolving in this thread. Our developmental circuits appear to be very similar to those being discussed here, but we're using thermistor types other than the CL-XX series for inrush limiting along with a combination of an internal master fuse plus fusible-link devices on each of the three main current branches. The master fuse inside the Ballast Tube has a slightly larger rating than and is in series with the under-chassis fuse we include in standard Restoration work, intended to be a tamper-resistant backup for the standard fuse. The fusible-link devices are designed to show failure visibly and are positioned to allow inspection under a strong light source through the ventilated metal shell of the Ballast Tube.
Our standard Restoration procedure includes pigtail fuses under the chassis for AC Line and B+ branch circuits or a Custom option substituting a fuse block mounted in an inconspicuous location under the chassis or inside the HV cage making the fuses user-replaceable like tubes upon special request. Therefore, we designed our Ballast Tube substitute in such a manner as to utilize its internal protective devices as tamper-resistant emergency backup devices.