How much filtering required for DC heaters?

RockysDad · 27th February 2006, 08:04 PM

I think I need DC for my 5687 heaters on my Aikido pre-amp due to some slight humming and was wondering how much filtering is needed. I'm planning on using a bridge rectifier to just one 4700uF cap for smoothing out some of the ripple. Is this enough or do I need to add somekind of regulator ie. 7506? Is there a rule of thumb on how much filtering a DC heater circuit needs?

On a side note, I using four 5687 tubes and these guys get pretty toasty! I know they are power hungry just to fire up the heaters but are these tubes designed to last a long time running this hot?

SHiFTY · 27th February 2006, 08:41 PM

You might have an earthing problem. Try running the heaters off a 6VDC supply or battery, if the hum goes then start building a regulator.

Otherwise you should use multiple star grounds to connect the cathodes at one point, signal grounds at another, then heater grounds at another, then join them all together at the chassis at one point.

You could try connecting the heaters to ground with a 100 ohm resistor instead of directly. (I havent seen the schematic, so if they are raised above ground ignore this advice!)

leadbelly · 27th February 2006, 08:45 PM

Good thread on the subject:

Hum free 5687 AC filament supply, is it possable ?

27th February 2006, 08:04 PM	#1
RockysDad diyAudio Member Join Date: Sep 2003 Location: Bay Area, CA	How much filtering required for DC heaters? I think I need DC for my 5687 heaters on my Aikido pre-amp due to some slight humming and was wondering how much filtering is needed. I'm planning on using a bridge rectifier to just one 4700uF cap for smoothing out some of the ripple. Is this enough or do I need to add somekind of regulator ie. 7506? Is there a rule of thumb on how much filtering a DC heater circuit needs? On a side note, I using four 5687 tubes and these guys get pretty toasty! I know they are power hungry just to fire up the heaters but are these tubes designed to last a long time running this hot?

27th February 2006, 08:45 PM	#3
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	Good thread on the subject: Hum free 5687 AC filament supply, is it possable ? __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

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27th February 2006, 08:41 PM	#2
SHiFTY diyAudio Member Join Date: Jul 2002 Location: New Zealand	You might have an earthing problem. Try running the heaters off a 6VDC supply or battery, if the hum goes then start building a regulator. Otherwise you should use multiple star grounds to connect the cathodes at one point, signal grounds at another, then heater grounds at another, then join them all together at the chassis at one point. You could try connecting the heaters to ground with a 100 ohm resistor instead of directly. (I havent seen the schematic, so if they are raised above ground ignore this advice!)

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