Rectifier heater failure question

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

#1 Rectifier heater failure question

Post by Thermionic Idler »

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 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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Nick
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Location: West Yorkshire

#2 Re: Rectifier heater failure question

Post by Nick »

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.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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Thermionic Idler
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Posts: 1018
Joined: Sun Apr 22, 2012 8:22 pm
Location: Southsea

#3 Re: Rectifier heater failure question

Post by Thermionic Idler »

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 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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