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Old 4th May 2012, 07:25 PM   #1
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Default Basic 12AU7 heatrr question

Hi, I am very new to tubes and am a little confused about the different possibilities for connecting the heater. I am using a 12V DC supply. Do I just connect +12V to pin 4, ground pin 5 and leave pin 9 alone?

Also, how sensitive is he heater to the value of the input voltage? The supply I am planning on using is a wall-outlet 12V DC transformer. However, I've measired it to be about 17V DC. Is this an issue?

Thanks in advance.
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Old 4th May 2012, 07:41 PM   #2
DF96 is offline DF96  England
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12V between pins 4 and 5 is fine.

17V is not, although the voltage will probably drop under load. Try putting an 82 or 100 ohm 3W resistor across the supply and measure the voltage.
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Old 4th May 2012, 09:47 PM   #3
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I would say if you where using 2 12au7 you could run in
series across the tubes and get away with 17v.
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Old 4th May 2012, 10:03 PM   #4
DF96 is offline DF96  England
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17V will be too much for one and not enough for two.
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Old 4th May 2012, 10:16 PM   #5
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Sounds like he needs a new wall adapter.
should be able to source one easy enough that would give 12v.
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Old 4th May 2012, 10:27 PM   #6
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You could use a 12VAC supply. Not as common as DC supplies but there are a few on ebay.
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Old 4th May 2012, 10:36 PM   #7
Enzo is offline Enzo  United States
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The wall adaptor is not regulated. Unloaded it puts out the 17v, it will put out the 12 volts when loaded to its rated capacity. This is VERY normal.
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Old 4th May 2012, 11:53 PM   #8
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A very poorly regulated supply like this is common in wall warts, but isn't really ideal for valve heaters - too much drama. Do you have other options?

All good fortune,
Chris
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Old 5th May 2012, 12:47 AM   #9
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Hey,
Here's a cheap easy fix. 12.6V CT 3.0A Chassis-Mount Transformer with Leads - RadioShack.com with NTE NEV1500M25 - CAP-1500MFD 25V RADIAL Model:NTE NEV1500M25| Catalog #: 55047226 The transformer with a simple bridge rectifier, (four diodes) and one cap to keep up the voltage and remove most of the residual AC. You will end up pretty close to 12 volts. You might have a Little AC but it won't be much and not enough to hear. Here's a link for rectifier designs, http://www.hammondmfg.com/pdf/5c007.pdf . I would install the parts and disconnect the high voltage. That way you just energize the heaters to check the voltage. Transistor based regulators are great but if the current draw is significantly less than transformer is capable of delivering it isn't necessary. IMHO.

My 2 cents

Last edited by mr2racer; 5th May 2012 at 12:58 AM.
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Old 5th May 2012, 01:45 PM   #10
DF96 is offline DF96  England
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I am still waiting for him to measure the voltage under load. It might be fine as it is.
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