Malfunctioning SRS?

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Malfunctioning SRS?

Post by Tom » Wed Aug 03, 2011 7:46 pm

I'm sure most of you have experienced times when T12s have failed to strike on SRS and just had the cathodes glowing as if they were T8s and need a bit of switch-flicking encouragement!

I know this can happen in the cold but however I've seen this happen in normal temperatures, the most recent being a nice old install of old SRS 6' Pop Packs which Kev showed me the other night! These all had various old Thorn, Philips and Osram T12s which appeared to be in a good, aged condition and a fair few were not firing up!

I know a bad earth can be a cause of this, as well as dirty tubes, but I'm wondering if aged/faulty capacitors may be to blame?

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Re: Malfunctioning SRS?

Post by SuperSix » Wed Aug 03, 2011 8:12 pm

Old capacitors can indeed be to blame, they degrade with time and the capacitance often falls. As you know the capacitor forms part of a series resonance circuit and if it's performing out of spec resonance may not occur and you often get a dimly glowing tube or dimly glowing cathodes. The other mode of failure with the capacitors is a dead short, which would allow immense amounts of current to flow through the cathodes, fortunately the fuse inside the fitting normally blows before the tube is destroyed.

If they're refusing to start you should obviously check the earth connection, make sure the tubes work and that they are clean and free from moisture but it seems that's all been ruled out. The problem will certainly be failed capacitors and possible failed fuses! ;)

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