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Renron 30th October 2007 05:20 PM

Help with Aikido B+ Bias layout
2 Attachment(s)
Being new to electronics and valves as well, I am willing to look ignorant ('cause I am) and ask stupid questions.
This is easy as pie to most of you, but to some of us it is confusing. I asked some questions on another thread but didn't want to hijack it. It is apparent that I am not alone in not understanding the B+Bias thing.
I am building an Aikido Linestage PreAmp with ECC802s, I purchased John Broskie's PCB kit and am almost ready to start slinging solder. I have used PSDII to design a full wave PS with minimum ripple. I have read and read but just can't quite grasp the B+ Bias to heater layout. My Transfomer has CTs on B+, 6.3V & 5V.

Please give me a hand with the drawing I've posted. Fire away:dead: Tell me What's wrong. Please!
Do I need D1 and D2?
What size R should I use for the safety drain from B+ to Ground?
Thanks to the Wizards of Valves for your help.

woodturner-fran 30th October 2007 05:59 PM

That looks right to me - I forgot what SY had said about using a trim pot in series with a R. Listen to him, not me!!!!!

Don't know about the diodes.


Renron 30th October 2007 06:26 PM

Thanks for your help, I took your advice and changed the B- side.:)
Any Ideas about the safety to ground?

I had the pleasure to meet SY (Stewart) at Burning Amp, even in person I had a hard time following what he said. :xeye: :xeye:
Not really, very smart guy and nice too!


Renron 30th October 2007 07:12 PM

2 Attachment(s)
Thanks for the input.
I have removed the trim pot from the voltage divider. I misunderstood it's placement and purpose. Got it now, thanks.
I removed the diode and leg off the B+ Center Tap, CT now goes to chassis ground. Right?
Is D2 needed? (My "Guess" is no.) As changed now, heater is floated. (not grounded to chassis)
Lookin' any better?
Thank you for the help.


pchw 30th October 2007 07:48 PM

Hi Renron,

Sy and many contributors of this forum are simply at the level that I can only imagine. Many techniques/knowledge that are trivial to them are probably rocket science to you and me :-)

The new diagram is much better, now back to the heater wiring, you don't get 12.6VDC with a diode in the CT. Ignore the voltage divider and just look at the heater circuit for the moment, the voltage between the CT and the top leg is 6.3, and 6.3 between the CT and the lower leg. If you want 12.6VAC, then ignore the CT and just use the top and lower legs of the heater transformer. If you want to 12.6VDC, then the cheap way to do is to use a fullwave bridge rectification followed by a CR section, The C will bring up to approximate 16VDC, and the R is to drop it back to 12.6, or replace the R by a regulator.

In terms of safety ground, only one recommendation, use 3 wire power code and make sure the ground wire is connected to the chassis. You can search Charlie's threads, there are good discussion of how to connect the chassis ground and the circuit ground. The ground in your diagram is the circuit ground.

Renron 31st October 2007 12:46 AM

You Rock!
Duh! That was a stupid mistake I make with the 6.3 and 12.6 full wave. I had a test jig set up yesterday using a bridge rectifier! I confused myself. I am using a ultra fast stealth diode on the B+ side and intended to use a bridge rectifier on the heater side so I have 12.6 available............Focus Luke .......Mmmmm.....Do it you can. Humor

I'll search some of Charlie's threads. Thanks.
I'll fix the layout and repost for more wonderful critiques.


Renron 31st October 2007 01:48 AM

2 Attachment(s)
How about this one? Any better? :o


pchw 31st October 2007 02:36 AM

Hi Ron,

The diagram is correct, but you still don't get 12.6 VDC, Am I pain in the butt :-) If you connect the load (tubes) right after the bridge rectifier, you can only get roughly 90% of the VAC minus the voltage dropped by 2 diodes. In this case, it will be something like 12.6 * 0.9 - 1.4 = 9.94 under load!!!! I suggest you to start with AC heater supply first and spend more time on the B+. At the current form, the B+ has no filtering at all. It is going to hum big time. If you haven't, download psud2 from to start the PS design :-)

Renron 31st October 2007 05:00 AM

2 Attachment(s)
Damn it Fred! Your're a Pain in the Butt!....So when we meet at next years Burning Amp festival....I'll buy ya a beer for your help. ;)

I have filters already planned out with PSUDII. Both for the B+ and the Heater supply. Thank you.

Renron 31st October 2007 05:09 AM

2 Attachment(s)
And the heater circuit.
I presume it does not have to be as ripple-free as the B+, as AC is used commonly for heater currents.
As always input (good or bad) is very welcome.


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