Need help changing 12V heater to 6V

phrarod · 8th April 2010, 09:34 PM

I want to use a different tube that uses a 6.3V filament. I have a 12.6V supply but the reg is adjustable.

What resistor changes ie values do I need for the resistor divider network that is in there now. It has a 200R and a 2K. Schematic attached.

Much appreciated!

tomchr · 8th April 2010, 10:02 PM

Quote:

Originally Posted by phrarod

I want to use a different tube that uses a 6.3V filament. I have a 12.6V supply but the reg is adjustable.

What resistor changes ie values do I need for the resistor divider network that is in there now. It has a 200R and a 2K. Schematic attached.

The regulator is an LM317T (made by National Semiconductors and many others). You can calculate the resistors needed for a given output voltage by following the equation on pages 1 and 9 of the LM317 data sheet.

~Tom

phrarod · 8th April 2010, 10:22 PM

Thanks Tom! My math is horrible but I give it a go since the formula is there. I have values in there as reference for calculation for 12.8V

Gorgomat · 8th April 2010, 11:02 PM

LM 317 Calculator

Matt.B.H. · 8th April 2010, 11:12 PM

I dont know what current you need? but be sure you dont run the 317 too hot

Cheers Matt.

phrarod · 8th April 2010, 11:41 PM

WOW! The calculator is awesome. Looks like R2 or in my case R11 is 810R I get 6.3V

I don't think it will run too hot.

wakibaki · 9th April 2010, 12:52 AM

Quote:

Originally Posted by phrarod

I don't think it will run too hot.

How much current?

If the tube is equivalent, then the current will be ~double that in the original circuit. The voltage dropped across the 317 will be 6.3 volts higher. So the dissipation in the 317 will be ~4 times the original.

Has it got a heatsink? 400% could be too much...

w

phrarod · 9th April 2010, 01:22 AM

It does have a heat sink. I need to investigate this. Thanks for the reality check on this.

phrarod · 9th April 2010, 03:08 AM

I was using a 5965 and will be moving to a tube with the following specs:

Uf = 6.3V, If = 350 mA uM = 25 Ia = 10.5 mA S = 6.8 mA/V Pa = 1.5 W

I have two filament supplies. One for each tube.

phrarod · 9th April 2010, 05:22 AM

One last question. If I do run into heat issues with the reg can I go to a LM335T and have the same voltage divider resistor values?

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8th April 2010, 10:22 PM	#3
phrarod diyAudio Member Join Date: Aug 2005	Thanks Tom! My math is horrible but I give it a go since the formula is there. I have values in there as reference for calculation for 12.8V

8th April 2010, 11:02 PM	#4
Gorgomat diyAudio Member Join Date: Aug 2009	LM 317 Calculator

8th April 2010, 11:12 PM	#5
Matt.B.H. diyAudio Member Join Date: Jul 2009 Location: Cheltenham	I dont know what current you need? but be sure you dont run the 317 too hot Cheers Matt.

8th April 2010, 11:41 PM	#6
phrarod diyAudio Member Join Date: Aug 2005	WOW! The calculator is awesome. Looks like R2 or in my case R11 is 810R I get 6.3V I don't think it will run too hot.

9th April 2010, 01:22 AM	#8
phrarod diyAudio Member Join Date: Aug 2005	It does have a heat sink. I need to investigate this. Thanks for the reality check on this.

9th April 2010, 03:08 AM	#9
phrarod diyAudio Member Join Date: Aug 2005	I was using a 5965 and will be moving to a tube with the following specs: Uf = 6.3V, If = 350 mA uM = 25 Ia = 10.5 mA S = 6.8 mA/V Pa = 1.5 W I have two filament supplies. One for each tube.

9th April 2010, 05:22 AM	#10
phrarod diyAudio Member Join Date: Aug 2005	One last question. If I do run into heat issues with the reg can I go to a LM335T and have the same voltage divider resistor values?

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