Rectifier heater failure question

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Thermionic Idler
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Joined: Sun Apr 22, 2012 8:22 pm
Location: Surrey

Rectifier heater failure question

Post by Thermionic Idler » Sun Jan 07, 2018 4:28 pm

Hi all,

Getting my old JuicyMusic Blueberry valve preamp ready for sale, found that it kept blowing the main power supply fuse at switch-on. Could not identify any burnt out components, then decided to test the valves on a (pretty basic) valve tester, starting with the 12X4 rectifier.

The tester indicated that the heater on the rectifier had gone open circuit. I replaced the 12X4 with a spare that tested okay on the heater, and the unit switched on successfully and remained on without blowing the fuse. I still need to put it in the rack and test it with audio, however.

What I can't work out is why a failed rectifier heater would lead to the fuse blowing - I thought that the valve would just simply not conduct - so you wouldn't get HT to the rest of the circuit. Possibly heater to cathode short?
Deck: Garrard 301
Audio Origami PU7
Van Den Hul Black Beauty
Phono: Whest PS30RDT
Pre-amp - Scratch built AMB α24/LCDuino
Amp - Transcendent "Son of Beast" 15W OTL
Speakers - FF225WK Metronomes

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Nick
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Location: West Yorkshire

Re: Rectifier heater failure question

Post by Nick » Sun Jan 07, 2018 6:54 pm

Only a guess, but maybe the failed heater fell onto the anodes shorting them. Removing the valve fro the amp has caused them to fall to the bottom of the valve, so you don't see the short any more.
Resistance isn't futile it's V / I.

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Thermionic Idler
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Posts: 467
Joined: Sun Apr 22, 2012 8:22 pm
Location: Surrey

Re: Rectifier heater failure question

Post by Thermionic Idler » Tue Jan 09, 2018 10:36 pm

Thanks Nick - I did wonder if it was down to some part of the heater filament touching another part internally, if it had broken. It all tested out fine this afternoon in any case.
Deck: Garrard 301
Audio Origami PU7
Van Den Hul Black Beauty
Phono: Whest PS30RDT
Pre-amp - Scratch built AMB α24/LCDuino
Amp - Transcendent "Son of Beast" 15W OTL
Speakers - FF225WK Metronomes

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