Wiring up 3 6.3 Volt Heaters to a 12V supply - Page 2 - diyAudio
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Old 18th January 2013, 03:00 PM   #11
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Just look at the schematic and look at the relative voltages of the cathodes with each other.

I'm scare mongering a bit, it's unlikely but it's worth looking into especially when some designs have heaters lifted above 0V.
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Old 18th January 2013, 03:24 PM   #12
akimmet is offline akimmet  United States
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Each 6bq7a uses 400mA each. That is 1.2A total. Lets not for get the inrush current involved with cold tubes, I don't doubt each tube's current draw would exceed 1A when cold.

A LM317 can barely handle 1.5A in absolutely prefect conditions. In practice I only trust them up to 1A. I would recommend if you wish to go this route, you have a voltage regulator for each tube. Each voltage regulator would in turn need a fairly large heat sink.
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Old 18th January 2013, 03:52 PM   #13
palmas is offline palmas  Portugal
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Quote:
Originally Posted by akimmet View Post
Each 6bq7a uses 400mA each. That is 1.2A total. Lets not for get the inrush current involved with cold tubes, I don't doubt each tube's current draw would exceed 1A when cold.

A LM317 can barely handle 1.5A in absolutely prefect conditions. In practice I only trust them up to 1A. I would recommend if you wish to go this route, you have a voltage regulator for each tube. Each voltage regulator would in turn need a fairly large heat sink.
Use 3 317 or use one TL1083
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Old 18th January 2013, 04:49 PM   #14
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Or a LM350. Or just buy the module I mentioned. It's cheap, already assembled and needs no heatsink!
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Old 18th January 2013, 05:05 PM   #15
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You could use one of these. Tube Filament Regulated Supply Soft Start Kit | eBay
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Old 18th January 2013, 05:41 PM   #16
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Originally Posted by supersonik319 View Post

Each heater takes 0.4 amps, so at 12 volts, I should use a 30 Ohm, 5Watt resistor, just to confirm:

+12V ---^--^--- GND
+12V ---R--^-- GND
Am I missing something? At 12 - 6.3 = 5.7V drop across the resistor and 0.4A current, I get 14.25 ohms (and 2.28 W)
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Old 18th January 2013, 08:16 PM   #17
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Why not keep it simple. Fit a 15 ohm resistor in series with each heater. Bridge each resistor with a higher value to get 6.3v on each heater. This way, the cold inrush current is limited as well.
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Old 18th January 2013, 08:49 PM   #18
DF96 is offline DF96  England
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And you waste about 7W, instead of 2.4W by doing it properly.
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