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Old 13th March 2007, 01:49 AM   #1
senderj is offline senderj  Hong Kong
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Default Regulator for tube pre

I want to build a pre-amp with 12AX7 X2 and 2AU7 X2. I find this regulator that come along with the pre schematic. But it did not indicate the current load of each output of the tranformer. It may be a piece of cake of experienced, but not for a newbie like me. Can anybody help me figure out the current required? Thanks.

NB. the 12V output at the left side is for the output delay.
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Old 13th March 2007, 02:01 AM   #2
SY is offline SY  United States
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I can't say precisely without the actual preamp schematic, but if it's like the other 99% out there using those tubes, for the high voltage, figure 1mA for each 12AX7 section, 4-5mA for each 12AU7 section. Each tube has two sections in its envelope. I'll leave the totaling to you.

Heaters run 0.15A total per tube.
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Old 13th March 2007, 09:26 AM   #3
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Hello

Because you did not post the schema, so not easy to tell you exactly current needed. However i could guest basing on quantity of tubes which may not more than 45mA for both chanel, therefore if i were you, i will choose the transformer:

15V/1A
6V3/1A
280V/70A

Rgds.
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Old 13th March 2007, 10:22 AM   #4
ulibub is offline ulibub  France
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Hello!

I would replace the bipolar transistor by a mosfet. I recommend using the type IRFI 840 G. Base resistor changes into a gate resistor at the same position, but you can take a value largely above 100 kOhm - I went as high as to 4.7 Mohms. Put a condenser parallel to the zener diodes. Depending on the time constant of the gate resistor - condenser array, you do not only get a perfect ripple rejection, but also a slow switch-on characteristic of the output voltage. Put a 470 ohms resistor directly in front of the gate pin to prevent any self-oscillations - like a grid stopper on a tube grid. Use a 47 uF capacitor between output and ground.

This mosfet stands 500 V and 4.6 A, 40 W max. dissipation. It is in a fully isolated package which stands up to 2.5 kV, so you even don't need a silicone or mica tab for mounting on heatsinks (or chassis). I use this layout also in the power supplies of my 6C33CB Circlotron amp with peak currents up to 500 mA. Works perfectly.

Greetings,

Uli
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Old 13th March 2007, 11:17 AM   #5
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Sorry for my typping error, i mean 280V/70mA are OKie.

By the way, in my opinion, the good choke more than 10Henry with 01 Oil Cap and 01 Polypropylene are very better than any solid regulator circuit, the sound will be more naturally.

Rgds.
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