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Vintage threads from the first ten years

previous: Ken FWIW, I've never seen a tube with i... -- 8/16/1999 8:03 PM

Re: Zener filament protection

8/18/1999 1:10 AM
moocow	Re: Zener filament protection You're right, it doesn't seem likely that the plate could short to the heater, but something like this happened to me. There was some kind of output tube failure that caused both 100 ohm heater resistors to explode (they were A-B carbon composition 'flameproof' resistors. Apparently 'flameproof' does not guarantee 'shatterproof'). I don't know if it was a plate to heater short, maybe it was the screen grid that shorted to the heater. Also, the plate pin (3) is right next to a heater pin (2), so a probe can slip and induce a plate to heater short. I've done this before and a metal oxide heater resistor burned out. No explosion this time. As for the Zener, my guess would be that the Zener would just get blown up if the plate shorts to the heater.

8/18/1999 1:10 AM

moocow

Re: Zener filament protection

You're right, it doesn't seem likely that the plate could short to the heater, but something like this happened to me. There was some kind of output tube failure that caused both 100 ohm heater resistors to explode (they were A-B carbon composition 'flameproof' resistors. Apparently 'flameproof' does not guarantee 'shatterproof'). I don't know if it was a plate to heater short, maybe it was the screen grid that shorted to the heater.

Also, the plate pin (3) is right next to a heater pin (2), so a probe can slip and induce a plate to heater short. I've done this before and a metal oxide heater resistor burned out. No explosion this time.

As for the Zener, my guess would be that the Zener would just get blown up if the plate shorts to the heater.

Replies:

Doc If the locating peg gets broken off... -- 8/20/1999 6:41 PM