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Old 6th April 2007, 06:41 PM   #1
Klimon is offline Klimon  Belgium
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Default Tube filaments in series?

Dear tube-lover,

Is it detrimental for tubes of same type and make to wire their heaters in series (e.g. to suit two 6.3V tubes with a 12.5 supply)? I know some tubes have a certain affix indicating their suitability for heaters connected in series, what about your average tube?

Cheers --- Simon
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Old 6th April 2007, 06:47 PM   #2
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Location: Paris - France

Go for it, without any problems, but make sure you replace the tubes in pairs...


Did live about 10 years in Canada
Back to France since the 1st February 2007.
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Old 6th April 2007, 06:56 PM   #3
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Scott integrateds wired 4 12ax7s in series and powered them with DC. Only the very early Scotts used AC on their heaters. Also the Dyna PAS preamps use a higher voltage DC and series the heaters... It works fine.....
The stuff you don't know always humbles us.........
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Old 6th April 2007, 06:58 PM   #4
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I agree with Alain. You should be fine using a pair of tubes from the same production run.

Controlled heater warm up time is important in lengthy strings of dissimilar types rated for the same heater current. None of the heaters get overvoltaged.
Eli D.
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Old 6th April 2007, 09:19 PM   #5
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Supporting this - best way to get dc on heaters with proper filtering (low current, high voltage). One must just watch the maximum heater-cathode voltage rating if several are used in series.
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Old 7th April 2007, 03:22 AM   #6
mach1 is offline mach1  Australia
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Some of the odd-voltage variants of common tubes have controlled heater warm up characterisitcs (usually around 11 secs) specially made for series wiring.

You can sometimes get 3V filament versions for a song and series heat them from a regular 6.3V tap.

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Old 7th April 2007, 07:12 AM   #7
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Some of us are old enough to remember directly heated TV sets.

All the tube heaters strung together in series across the mains.

No mains transformer and live chassis

Great fun!
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Old 7th April 2007, 09:16 AM   #8
Klimon is offline Klimon  Belgium
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That's a clear answer, and luckily the one that opens possibilities!

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