Regulated Heater on the 6SN7 Aikido Plate to Heater question - diyAudio
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Old 22nd November 2009, 04:07 PM   #1
john65b is offline john65b  United States
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Default Regulated Heater on the 6SN7 Aikido Plate to Heater question

I know this topic has been discussed ad nauseum, but I have searched a few ways and cannot see my exact issue.

I have an all 6SN7 Aikido. The B+ should be in the range of 250V to 275V (still wiring everything up). I elected to use a separate 6.3 -0 -6.3 tranny for the heaters, and the Aikido board is set up for 12V heaters. All good.

I started wiring up the rectified heater with a cap and then a 7812 regulator. All good. At this point I grounded the ground pin of the 7812 and that was to be my heater ground, but I totally forgot that I must raise the heater to 1/3 B+ to be within the max heater to plate voltage.


At a B+ of 275 (worse case) I have a plate voltage of 275/2 = 137.5 and if my rectified/regulated heater is at 12vDC, I have a heater to plate voltage of 125.5V, which is under the 200V max...so I should be ok, correct?

BTW - I have seen 100v and 200v max h-k voltage too...don't know which is correct...

If not OK, I should lift that center pin ground connection of the 7812 regulator and put the 300R/100R with cap to raise my heater?

I am using the 6.3 0 6.3 tranny and the 7812 simply because I have them.

Like I said, I have searched, but cannot find a reference to the 7812 regulator in my case.
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Last edited by john65b; 22nd November 2009 at 04:17 PM.
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Old 22nd November 2009, 04:16 PM   #2
john65b is offline john65b  United States
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Also, would a 25k Noble pot be OK for the attenuation control of the Aikido, or a 100k better?
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Old 22nd November 2009, 05:27 PM   #3
piero7 is offline piero7  Italy
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Here, just connect the 1/4 B+ to the negative of you filament supply
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Old 23rd November 2009, 08:23 PM   #4
john65b is offline john65b  United States
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OK, I understand,

The question is do I lift the earth grounded Ground pin of the 7812 regulator and place it on this 1/4 B+ ground point?
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Old 23rd November 2009, 08:42 PM   #5
tomchr is offline tomchr  United States
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Here's an idea: Use a full-wave rectifier connected with the "AC IN" pins to the 6.3 V taps on the 6.3-0-6.3 winding. The "-" of the bridge rectifier goes to the GND pin of the 7812 (via reservoir cap of course). The "+" output of the bridge rectifier goes to the input pin of the 7812 (via cap). Then you have a floating 12 V supply for the heaters. You can elevate this by connecting the center tap of the 6.3-0-6.3 to the appropriate voltage level.

One issue, though: Depending on your heater current, you may need a very, very large reservoir cap in your heater power supply. I'd run a simulation or at the very least a calculation of the ripple voltage to make sure it doesn't drop below the minimum required by the 7812 (2.5 V drop-out AFAIR --> 14.5 V min input voltage needed).

~Tom
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Old 23rd November 2009, 10:36 PM   #6
john65b is offline john65b  United States
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Tom,

Your post is EXACTLY like I have it, except I have a 2200uf cap between the rectifier and 7812. The 7812 center pin (ground) is left floating and not connected to ground in any way?

So the Tranny CT is the only connection raised by 1/4 B+ with voltage divider and not the 7812 center pin?. This is my main question.

I have raised the Heater ground from a 275v B+ before on other preamps with a 100k (1/2W) and 20k (1/2W) and wonder if I can use this instead of the 300k (2W) and 100k (1/2W) as I do not have a 300k (2W).

I am running the Aikido with all 6SN7 so heater current should be around .6 + .6 = 1.2 amp.
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Old 24th November 2009, 05:44 AM   #7
john65b is offline john65b  United States
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OK, I abandoned the idea of the 7812 since its only good for 1A. I dumped the 7812 and put in a 3 ohm resistor. I get 12.3VDC. Perfect.

I decided to "float" the heater round by putting a .1 uf 600V PP cap from earth ground to the heater ground at 2200uf cap neg pin. I checked the heater to cathode voltage and it varies from 50v to 70v....which is good. Plugged her in and there is no hum and sounds great...more critical listening tomorrow.
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