6.3V/5A DC Fillament Schematic

[LinuksGuru]

Anyone have ready to use schematic of high-efficient stabilized DC filament 6.3V/5A?

It will be used for integrated amp with 7 x 12AX7 (6N2P-EV) tubes which includes phono-preamp (very sensitive to hum)? Actually 3A will be enough, but for reserve it should handle 5A without overheating. 6N2P although directly compatible with 12AX7 do not support 12.6V filament unfortunately.

Please do not suggest classic baby schematic with one zenner diode and one transistor :-)

What input voltage would you recommend? Will 8V AC be sufficient? 8V AC, 10000uF filter cap, 3A, will have 3V ripple, V(DC) = 9.78V before SS stabilizer.

Any suggestion(s) will be greatly appreciated. Thanks in advance.

[gruni]

you could start with this regulator: http://www.elecfree.com/electronic/w...al-circuit.jpg

and raise the output by 1.3v by adding two diodes between ground and the gnd-connection of the 7805 regulator, resulting in 6.2v and a bit of underheating...

[nigelwright7557]

The problem with that much power is it will need a hefty regulator and heatsink.

I must admit I have gone for DC heaters in my pre amps and amps just for that little less hum.

[LinuksGuru]

Looks like there are 2 very simple choices:
1) 5A IC voltage regulators, LM138/238/338, and LM1084
2) High-Efficiency step-down switching voltage regulators, like LM2678

LM2678 requires much much smaller heatsink, but since it uses 260 KHz switching frequency it may emit extra noise.

What would be your choice?

[SpreadSpectrum]

Use an LM338. See data sheet for circuit. You will need a good sized heatsink.

I also just made a 6.3V regulator with a 6.3V NJM2396. Very simple circuit and isolated case. Obviously, you need more than one for 5A.

Also, these high current low volt supplies need to be built with care as you can easily introduce other noises(switching etc.) that will introduce more noise that the AC would have. It is non-trivial to make a good clean high current DC supply.

[Stixx]

Last year I built a LM1084 based regulator to supply 2.8A at 6.3V for my Aikido headamp (as per the common schematic). It sports heavy heatsinking and works troublefree ever since.

[ChrisA]

Originally Posted by LinuksGuru

Anyone have ready to use schematic of high-efficient stabilized DC filament 6.3V/5A?
Please do not suggest classic baby schematic with one zenner diode and one transistor :-)

I think those three tab regulators are so cheap and work so well there is not reason not to use several of them. So the Schematic I'd try would be...

1) Rectify and filter the AC to a unregulated 8V using diodes and capasitor.

2) Place a three terminal adjustable voltage regulator near each tube or group of tubes. Use the LM317. Placing regulators near the the load is an old technique. I think they call it "distributed regulation" and results in very quiet DC as the regulator presents a high impedance to noise and it is actually cheaper than building a large high current DC regulater. It will also provide very high degree of isolation between the stages. Not that you really need any of this in a DC heaters

The lm317 was features that are hard to implement with a build it yourself, thermal and overcurent shutdown and so on. The lm317 is very easy to use.

OK if you want one big supply the lm317 data sheet shows how to build your "baby" ciruit but using and 317 in place of the zenier. But as I said, I'd rather just use three lm 317s, each driving it's own load.

[ChrisA]

Originally Posted by LinuksGuru

.... but since it uses 260 KHz switching frequency it may emit extra noise....

My hearing is not so good any more and I can't hear anything above 200Khz. I doubt I would notice the noise.

OK, more seriously, A high switching frequency is a good thing, the higher the better because you can use smaller components in your filter. 60Hz is actually harder to filter out. If you are very worried about this, build the supply inside one of those cast aluminum Hammon boxes and bolt the regulator to the inside of the box, using the box as both a heat sink and shield.

I forgot to say this in my other post: My solution was to use DC heaters only for the preamp and use AC for the larger tubes. Then just one lm318 is enough. Use a center tapped 12V transformer, send 12V to the regulator to drive the DC supply and then 1/2 of the 12V to each of the power tubes. This works well, the more sensitive tubes get DC and you have two 6.3V AC strings each with 1/2 the current.

[Minion]

If you look in the LM317 Datasheet it shows how to make a 5A adjustable Voltage regulator curcuit useing the LM317 and a Pass transistor (2n3055 ??)

it only uses a few extra parts and seems to work well , I built a 24v 5a one for a huge rack of preamps , I think I might even have a PCB design somewere ....


Cheers