referencing heater supply ground to B+

jarthel · 12th March 2007, 11:44 PM

I've seen circuits where the heater supply ground is reference to B+.

I've seen people used 1/4B+ or 1/2B+.

how do I determine the right ratio?

I'll be using a 6CG7 and according to this datesheet (http://www.mif.pg.gda.pl/homepages/f...093/6/6CG7.pdf),

the heater voltage with respect to ground:
DC component: 100V
total DC and peak : 200V

My B+ is 150V. I'm wondering if it's a good idea if I use 2x 100K resistors (thus referencing my heater to 1/2B+ = 75V)

Thank you.

ray_moth · 13th March 2007, 02:22 AM

If you want to bias the heater to minimize hum, decide at what voltage the cathode will be, then bias the heater to be about 35v more positive than that.

A potential divider from B+ to ground, as you describe, but with resistances totalling about 1/2 megohm, should do. Bypass the lower resistor of the PD with a 10uF cap (of adequate working voltage).

Merlinb · 14th March 2007, 07:39 PM

It depends on what voltage the cathodes are at in the amp you're using. If they're all at a couple of volts then you can reference your heaters at anything up to abotu 50V, so as Ray said, 35V is a good choice, it's not critical.

However, if there's a cathode follower, or LTP or something in there, then one or more of your cathodes will be at a high voltage. The idea is to then place the heater voltage so it doesn't exceed Vhk for any of the valves. In your case I don't think it's a problem- your HT is only 150V.

The only consideration is that valves have a maximum heater-cathode resistance. It's not always quoted, and it doesn't seem to be that critical, but for piece of mind you shouldn't make the lower resistor in the divier any greater than 100k. I usually shoot for 10k to 47k and a reference voltage of about 30V.

12th March 2007, 11:44 PM	#1
jarthel diyAudio Member Join Date: Jan 2002 Location: somewhere in Australia	referencing heater supply ground to B+ I've seen circuits where the heater supply ground is reference to B+. I've seen people used 1/4B+ or 1/2B+. how do I determine the right ratio? I'll be using a 6CG7 and according to this datesheet (http://www.mif.pg.gda.pl/homepages/f...093/6/6CG7.pdf), the heater voltage with respect to ground: DC component: 100V total DC and peak : 200V My B+ is 150V. I'm wondering if it's a good idea if I use 2x 100K resistors (thus referencing my heater to 1/2B+ = 75V) Thank you.

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13th March 2007, 02:22 AM	#2
ray_moth diyAudio Moderator Emeritus Join Date: Jan 2004 Location: Jakarta	If you want to bias the heater to minimize hum, decide at what voltage the cathode will be, then bias the heater to be about 35v more positive than that. A potential divider from B+ to ground, as you describe, but with resistances totalling about 1/2 megohm, should do. Bypass the lower resistor of the PD with a 10uF cap (of adequate working voltage).

14th March 2007, 07:39 PM	#3
Merlinb diyAudio Member Join Date: May 2006 Location: York	It depends on what voltage the cathodes are at in the amp you're using. If they're all at a couple of volts then you can reference your heaters at anything up to abotu 50V, so as Ray said, 35V is a good choice, it's not critical. However, if there's a cathode follower, or LTP or something in there, then one or more of your cathodes will be at a high voltage. The idea is to then place the heater voltage so it doesn't exceed Vhk for any of the valves. In your case I don't think it's a problem- your HT is only 150V. The only consideration is that valves have a maximum heater-cathode resistance. It's not always quoted, and it doesn't seem to be that critical, but for piece of mind you shouldn't make the lower resistor in the divier any greater than 100k. I usually shoot for 10k to 47k and a reference voltage of about 30V.

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