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SRS Ballasts
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Many thanks to Aaron for sending these over.
One ballast is shown here running a HO lamp. It starts sorta like a rapid start but the tube needs to be grounded to start. I believe regular HO RS ballasts has a really high OCV (450-500v) so it just instant starts if the reflector isn't grounded. Oddly the lamp also flickers for about half a second after starting during which the step up buzzed loudly but ran normally afterwards.
SRS (Semi Resonant Start) ballasts were commonly used in Britain if a starterless ballast was desired. Rapid start was not used because of the costs of adding cathode heating transformer to a choke ballast (120v 4' ballasts needed a built in step-up anyway so it was trivial to add the cathode heating circuit). See here for more info.
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(i have 9 more up for free left)
As I was stripping one ballast down for repainting, it turns out that these are rebranded by Ardco. The original manufacturer is a company called. It turns out they're actually a 240v 50hz European SRS ballast for 5' 65w T12 lamps.