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December 05, 2019, 04:47:45 AM

Author Topic: DC Filament supply : voltage too high  (Read 49 times)

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Offline davidnow

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DC Filament supply : voltage too high
« on: November 09, 2019, 05:50:18 AM »
Hi,
after completing the DC filament supply, i mesured the supply voltage : 2,7 on the A tube and 2,65 on the D tube.
As it is out of the 5% range, i am wondering which resistance i should replace/add.
Thanks for help
David

Offline Deke609

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Re: DC Filament supply : voltage too high
« Reply #1 on: November 09, 2019, 06:01:18 AM »
Before changing heater resistors, it's worth looking at your mains voltage coming out of the wall and comparing it with the voltage range you wired the power transformer for (e.g., less than 115 or more than 115 but less than 130, etc.).  For example, mains voltage of 120VAC through a transformer wired for less than 115VAC will give you high filament heater voltages.

cheers, Derek

Derek
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Online Paul Birkeland

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Re: DC Filament supply : voltage too high
« Reply #2 on: November 09, 2019, 06:03:37 AM »
What's your line voltage?

What model of meter do you have?  Are the batteries fresh?

You are measuring between pins 1 and 4 on the 4 pin socket, not the lugs of the terminal strip?

I definitely have owned meters that wouldn't resolve low DC voltages like this very well, so that's why I ask.  Otherwise it will help to know what your line voltage is just to be sure. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline davidnow

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Re: DC Filament supply : voltage too high
« Reply #3 on: November 09, 2019, 06:24:19 AM »
Voltage is 237V tonight and i wired the transformer for more than 235V and less than 245V.
I use an autoranging multimeter that have worked flawlessly until now.
I mesured the voltage on the tube socket pins.
DAvid