Basic 12AU7 heatrr question

slacker4848 · 4th May 2012, 07:25 PM

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.

DF96 · 4th May 2012, 07:41 PM

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.

bigaudioscotto · 4th May 2012, 09:47 PM

I would say if you where using 2 12au7 you could run in
series across the tubes and get away with 17v.

DF96 · 4th May 2012, 10:03 PM

17V will be too much for one and not enough for two.

bigaudioscotto · 4th May 2012, 10:16 PM

Sounds like he needs a new wall adapter.
should be able to source one easy enough that would give 12v.

nigelwright7557 · 4th May 2012, 10:27 PM

You could use a 12VAC supply. Not as common as DC supplies but there are a few on ebay.

Enzo · 4th May 2012, 10:36 PM

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.

Chris Hornbeck · 4th May 2012, 11:53 PM

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

mr2racer · 12:58 AM

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

DF96 · 5th May 2012, 01:45 PM

I am still waiting for him to measure the voltage under load. It might be fine as it is.

4th May 2012, 07:25 PM	#1
slacker4848 diyAudio Member Join Date: May 2012	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.

4th May 2012, 10:27 PM	#6
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	You could use a 12VAC supply. Not as common as DC supplies but there are a few on ebay. __________________ http://www.murtonpikesystems.co.uk PCBCAD50 pcb design software.

5th May 2012, 12:47 AM	#9
mr2racer diyAudio Member Join Date: Jul 2009	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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4th May 2012, 07:41 PM	#2
DF96 diyAudio Member Join Date: May 2007	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.

4th May 2012, 09:47 PM	#3
bigaudioscotto diyAudio Member Join Date: Sep 2004 Location: North Carolina,	I would say if you where using 2 12au7 you could run in series across the tubes and get away with 17v.

4th May 2012, 10:03 PM	#4
DF96 diyAudio Member Join Date: May 2007	17V will be too much for one and not enough for two.

4th May 2012, 10:16 PM	#5
bigaudioscotto diyAudio Member Join Date: Sep 2004 Location: North Carolina,	Sounds like he needs a new wall adapter. should be able to source one easy enough that would give 12v.

4th May 2012, 10:36 PM	#7
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	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.

4th May 2012, 11:53 PM	#8
Chris Hornbeck diyAudio Member Join Date: May 2011 Location: Little Rock	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

5th May 2012, 01:45 PM	#10
DF96 diyAudio Member Join Date: May 2007	I am still waiting for him to measure the voltage under load. It might be fine as it is.

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