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Old 26th July 2010, 09:15 PM   #1
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Default Zener heater regulator

I realy like this zener heater regulator from Conrad Johnson using good quality capacitor… This schematic is from Premier 10 preamplifier, it is to drive two 6GK5 tube.
Do you think I can drive this tube with this schematic or I need to change something?

-One 12AU7 (300mA)
-One 12AX7 (300mA)
-Four EL84 (2x 800mA)
Total: 2.2A


2N3055 is good for 15A, this is not a problem but 681 Ohm is critical??? Maybe it is better to change the 4700uF for a much bigger value??

Thank you!
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Old 26th July 2010, 09:20 PM   #2
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Quote:
Originally Posted by arold19 View Post
I realy like this zener heater regulator from Conrad Johnson using good quality capacitor… This schematic is from Premier 10 preamplifier, it is to drive two 6GK5 tube.
Do you think I can drive this tube with this schematic or I need to change something?

-One 12AU7 (300mA)
-One 12AX7 (300mA)
-Four EL84 (2x 800mA)
Total: 2.2A


2N3055 is good for 15A, this is not a problem but 681 Ohm is critical??? Maybe it is better to change the 4700uF for a much bigger value??

Thank you!
It probably will work and the 681 ohms is not critical. But this is a very ancient circuit from the time that integrated regulators were not existing. A modern 12V LM7812-type regulator will perform much better, better regulaton and less noise and much smaller (a TO220). Maybe you should look into that too. You could even use individual regs for each tube.
I guess John Broskie has good circuits for that on his Tube Log site.

jd
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Old 26th July 2010, 09:49 PM   #3
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...or go for current rather than voltage regulation. Easier on the heaters at start-up.
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Old 26th July 2010, 10:04 PM   #4
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Very nice idea!
What do you think if I use 1 LM7812 for the 12AU7 and 12AX7, One for two EL84 and an other one for two EL84???
I think it will be very simple to do!
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Old 26th July 2010, 10:58 PM   #5
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This schematic will work fine???
What value is good for the input capacitor??? 12000 uF... more?
Oh, I forgot the negative reference on each 7812...
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Old 26th July 2010, 11:01 PM   #6
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[QUOTE=arold19;2254740]What value is good for the input capacitor??? 12000 uF... more?
QUOTE]

What ever the 78xx datasheet says...
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Old 26th July 2010, 11:09 PM   #7
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On some exemple at the end of the datasheet, we can see 0.33uF at the input and 0.1uF at the output...this is very very small for me... this have sence?
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Old 26th July 2010, 11:52 PM   #8
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The .33 and .1 caps are just for stability and should be mounted as close to the regulator as possible, and each regulator should get them.
The main filter cap size depends on the input voltage. The higher you go, the less uf you need, but high value caps in this voltage range are cheap enough to use brute force here.
I'd start with 2,200 uf and see what happens. That's the value I used in my homebrew guitar amps, but I just sent dc to the preamps and used ac for the finals.
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Old 27th July 2010, 01:34 PM   #9
Arnulf is offline Arnulf  Europe
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Quote:
Originally Posted by aardvarkash10 View Post
...or go for current rather than voltage regulation. Easier on the heaters at start-up.
arold19: do what aardvarkash said and forget the voltage regulation mumbo-jumbo. Depending on your input voltage you only need one power transistor per tube, a handful of resistors and a (small signal) reference transistor (or a pair of diodes or a LED or zener if you cannot find a suitable transistor anywhere in your junk box).

Read this check out section 5.0 in particular, the right current source type shown in figure 6a is what you should be looking for. Note that you can use your NPN transistors in place of PNP shown in this example if you turn the circuit upside down.
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Old 27th July 2010, 01:45 PM   #10
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Ahhh.... The on-line curse
Ask two questions, get three answers, all different. Who you're gonna believe? The one who shouts loudest, the one who says 'trust me!', the one who provides some logical explanation why his solutions is recommended?
Chicken and egg right?

jd
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