Agree, caps usually fail shorted. How about adding a fuse? If the cap shorted current would go way up and blow the fuse. A couple high rated Zener diodes would work but like everything else they only protect while diodes are good.
Norm
:After having read thoroughally your article about replacing defective line cords, I decided to tackle the job on my RCA 9TX. Although some experimenting is necessary for fine tuning the value of the capacitor, the job seems to be straightforward. What is worrying me is that unlike a resistive element, which usually fails in open circuit, a capacitor very often fails in shorted condition, which is a case for alarm, cos that means that all the valves are bearing the full mains voltage. And they will last a few seconds!!
:I have been browsing at other systems where zener diodes and current limiting devices are used to counteract this effect.
:Does Nostalgia Air have its own version to include such safety features, seeing that we do everything in our power to protect our beloved collectibles from such avoidable damage?
:
::After having read thoroughally your article about replacing defective line cords, I decided to tackle the job on my RCA 9TX. Although some experimenting is necessary for fine tuning the value of the capacitor, the job seems to be straightforward. What is worrying me is that unlike a resistive element, which usually fails in open circuit, a capacitor very often fails in shorted condition, which is a case for alarm, cos that means that all the valves are bearing the full mains voltage. And they will last a few seconds!!
::I have been browsing at other systems where zener diodes and current limiting devices are used to counteract this effect.
::Does Nostalgia Air have its own version to include such safety features, seeing that we do everything in our power to protect our beloved collectibles from such avoidable damage?
::
:
:
Right, Zener diodes operate on DC. For AC you can use two back to back, in series.
Some add a diode in series with the filaments. This will reduce voltage to arounmd 85. Adding a little resistance brings it down to around 65 which many radios require. Again a diode may fail shorted increasing filament to near full line voltage.
Interesting to think about but not worth the worry.
I do have one radio with series wired 215A's. I didn't want anything to happen to them so made a voltage regulated supply followed by a current regulator. If voltage increased current would be clamped.
Norm
:::Anton
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::: Agree, caps usually fail shorted. How about adding a fuse? If the cap shorted current would go way up and blow the fuse. A couple high rated Zener diodes would work but like everything else they only protect while diodes are good.
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:::Norm
:::So I take it that the best way to protect the tubes is to use a combination of a fuse and a zener diode. Once the voltage goes up more than required, the zener would start conducting making sure the fuse blows. The voltage across the tube filaments in my case is 68V. Do zener diodes exist in this voltage?
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::::After having read thoroughally your article about replacing defective line cords, I decided to tackle the job on my RCA 9TX. Although some experimenting is necessary for fine tuning the value of the capacitor, the job seems to be straightforward. What is worrying me is that unlike a resistive element, which usually fails in open circuit, a capacitor very often fails in shorted condition, which is a case for alarm, cos that means that all the valves are bearing the full mains voltage. And they will last a few seconds!!
::::I have been browsing at other systems where zener diodes and current limiting devices are used to counteract this effect.
::::Does Nostalgia Air have its own version to include such safety features, seeing that we do everything in our power to protect our beloved collectibles from such avoidable damage?
::::
:::Do Zener diodes work on AC? The voltage to these tubes is alternating?
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Is there any chance of having the citcuit you are using on your radio?
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