Schematic and parts list for DC heater supply?

[dehughes]

Hey all,

This is just in case I have to end up with DC heaters on my 6SN7 preamp.... I'm going to try a bunch of other stuff to get the hum out of that channel, but in case I can't, I'll try DC heaters as a last resort.

Is there a simple schematic and parts list for a DC heater supply? I know that the Komet Constellation uses two diodes and a 10000uf 25v electrolytic, but beyond that I'm in the dark.

THANKS.

[paulster]

Get an off-the-shelf bridge rectifier, something like this one (Fairchild GBU8B):
[img:217:200]http://cpc.farnell.com/productimages/fa ... 066991.jpg[/img]

These fit nicely in 3/32" eyelets.

AC goes in, 10,000uF 16-25V cap goes on the DC side.

Disconnect your heater centre-tap connection from ground and cap it off, and ground the DC 0V instead, and you should find that this is quieter than having the AC grounded. Make sure that if you try leaving your centre-tap connected to ground first that you don't ground the DC side or you'll be ordering a new bridge rectifier having just shorted out one side of it. It's an easy mistake.

Run your first 12AX7 stage and your 6SN7 off DC.

The ripple will still be reasonably high, but if you want to improve things significantly you'll need to go for a regulated supply which is more complicated as you'll need a low-dropout regulator and Schottky diodes to get 6.3Vdc with some headroom off 6.3Vac. It also ups the component count and complexity.

[Phil_S]

1) IMO, more work than it's worth.
2) Voltage will not come out right and you will need a way to drop it. This becomes a hassle.
3) You will reduce current (amps) capacity, so, if you insist, make sure the filament winding has enough reserve to handle the tube compliment.

While I could easily be wrong about it, I don't think this is going to solve your problem. Focus on what I posted today. This is a last resort and you aren't anywhere near having exhausted the possible cures. I have 10 amplifiers, all with a/c heaters and none hum. Yours isn't fancy enough to need DC heaters.

If you are hell bent to try this, find a DC wall wart that puts out about 6V @ 900mA and use this to power V1 and V2.

[jaysg]

Here's a PS section from an amp I built a while back. I've used the 5V rectifier winding for pre-amp heaters. The trick is that the rectifiers are Schottky diodes which only drop about 0.3V each.

[M Fowler]

Here is what I drew up.
I put bothe 9 pin and 8 pin in there so you know how it is hook up.

Mark

[dehughes]

Sweeeet..... Thanks guys.

The amp in question has a tube recto already, so Jaysg, I wager I'd be better off tapping into the 6.3v lines for this, yes? Also, what does the UF4007 diode right before the cap do?

So Mark, what type of diodes would I purchase for your design? Any particular ones? Also, I assume I'd just tap into the 6.3v heater winding as-is? (That is, lift the wires from the tube socket, run them to the diodes, then run wires back to the socket?)

[M Fowler]

Use a square four pin 25A bridge rectifier rather than individual diodes. The rounded off end is pos + or it maybe marked. Its you choice if you want to go with suitable individual diodes doesn't matter.

From filament supply to both sides of the 25 amp bridge rectifier. Top and bottom in picture.

The minus side of bridge goes to .1 mfd cap to ground.

To remove the ripple you need anything from 4700-10,000 mfd 16 to 25v cap from (-) to + of the bridge rectifier with + on cap towards + of the rectifier.

If the voltage is greater than 6.3 after the rectifier use a small value resistor (1 ohm) from + to the filament pin 7 on your power tube socket.

Yes you can use the 6.3 taps.

[jaysg]

I wager I'd be better off tapping into the 6.3v lines for this, yes? Also, what does the UF4007 diode right before the cap do?

Yup, this isn't going to help you much. The UF4007 drops an additional 0.6V. I'm not sure how much it matters, but I decided that 6.0 was better than 6.6V. I don't recall, but I probably replaced it with another 3A Schottky when I got more. This was used to provide DC heaters for two 12ax7's, so the 1A diode was seeing 600mA.

[Wayne]

Before you get too carried away - get yourself one of those square 6V lantern batteries & try running the preamp tubes' heaters with that. If it doesn't help, you'll know you're barking up the wrong tree.

W

[dehughes]

Before you get too carried away - get yourself one of those square 6V lantern batteries & try running the preamp tubes' heaters with that. If it doesn't help, you'll know you're barking up the wrong tree.

W

Oooooh, that's a great idea. Soooo good. Perfect. Thank you. I do get more carried away than I should when it comes to troubleshooting, so I'll see if I can tame this hum first via grounding/lead dress changes, and go with the lantern battery as a next step.

So, with a lantern battery, I'd just hook up one of the 6SN7 heater wires to the + and the other to the - terminal, and that's it?

[Wayne]

Yup - just disconnect the heater lines from the amp's heater supply and sub in your own 6 volts from the battery. You'll probably want to ground one side or the other (shouldn't matter which) wherever your heater supply center tap is grounded.

Good luck.

W

[dehughes]

Yup - just disconnect the heater lines from the amp's heater supply and sub in your own 6 volts from the battery. You'll probably want to ground one side or the other (shouldn't matter which) wherever your heater supply center tap is grounded.

Good luck.

W

Great. Thanks. So to be clear, the 6v + terminal from the lantern battery would connect to one of the heater pins, and the - terminal would connect to the other heater pin which would then be grounded to the same point as the 6.3v CT, yes?

[Wayne]

Exactly.

And do continue letting us know how it's going - it's much less frustrating learning through other's trials & tribulations!

W

[dehughes]

Exactly.

And do continue letting us know how it's going - it's much less frustrating learning through other's trials & tribulations!

W

HA. Yeah, I know....watching someone else build something is sometimes more satisfying than building it yourself...especially if there are problems that come up. I'll keep posting updates on that main thread (Brown Deluxe/Constellation...).

[dehughes]

IT'S FIXED!!!!!!!!!!!!!!!!!!!

It WAS the 6SN7 heaters all along! I clipped in a 6v lantern battery to the terminals of the tube, and ran a lead from the - terminal of the battery to the same point where I grounded the AC heater CT, plugged in, turned the amp on, and...


NOTHING.


Just a soft hum which I'd expect from a cloned Brown Deluxe tranny. WONDERFULLY silent. THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU.

SO, now, of course, I'm going to install DC heaters. Any recommended places? Newark? Mouser? I'll need to get diodes, the cap, and some solder tips for my Weller WLC100. I'd like to get a 10000uf 25v can cap with radial solder terminals. I'd then mount the cap inside the chassis a la the Constellation.


THANK YOU ALL SO MUCH!