Voltage Doubler / Heater Regulator

[stephenl]

I want to use a 6.3vct winding to feed a voltage doubler / regulator as shown below for a 12.6vdc heaters for my preamp tubes and also feed 6.3vac to the power tubes. Can I do it as shown below?

[diagrammatiks]

I don't think you can elevate like that.

there's a max dc for the relay coil.

[stephenl]

Relay coil?

[diagrammatiks]

my bad I thought you wanted to use it to power some relays. usually when people say 12.6v I think relays.

yes you can do that.

might want to use an low drop out regulator to make sure you hit the minimum drop out voltage under load.

[markr14850]

You might have a problem with mixing the grounds on the AC side (center tap) and DC side (75v ref). Usually you would only directly ground one of them, not both.

[stephenl]

Should have been obvious to me...I'll need to either cut the trace that connects the elevation to the heater (-) rail and connect the CT to the elevation, or just move the elevation circuit off board...

[markr14850]

Should have been obvious to me...I'll need to either cut the trace that connects the elevation to the heater (-) rail and connect the CT to the elevation, or just move the elevation circuit off board...

Try it both ways and see which is quieter.

Beware that taking voltmeter readings between the floating side and ground might blow your rectifiers.

In an ideal world, I'd go for a separate supply for the DC filaments, maybe even a switcher. On my prototyping board, I use this one: https://www.alliedelec.com/search/produ ... U=70069560. It has a tiny amount of HF noise on the output, so I set the voltage adjustment on it a bit high, and run a series 1 ohm resistor and then a large uF cap shunt to ground.

[Structo]

I'm wondering about the operation of the voltage regulator and if it needs a 0 volt reference.

[oldmacman]

Why do you need a voltage doubler? If you hook up the 12AX7 heaters in the conventional way, you should only need 6.3 VDC.

There's a regulated way to do it here: http://www.diytube.com/phpBB2/viewtopic ... 9df68f823c -- note that if you do it this way, make sure to get the ADJ version of the LM1084.

Also, you really shouldn't need DC heaters on your power tubes if you're running push-pull...[/url]

[stephenl]

In reply to oldmacman:

If you look at my pencil sketch in the first post, the power tubes are connected to 6.3 vac.

I'm trying regulated 12.6vdc to the preamp tubes because:

- heater wiring is slightly simplified.
- 1/2 the current will radiate a lower magnetic field which should radiate less noise. Regulated DC should be less noisy too.
- Just wanted to try something different.

In reply to structo:

I think it does need a "0" reference point. I think the best way to do it is to connect (only) the winding CT to the elevated reference.

[diagrammatiks]

you actually can't use the center tap on the winding.

6.3vac centertapped is only 3.65 per side.

You need to use the entire winding and elevate after the regulator.

[markr14850]

I think it does need a "0" reference point. I think the best way to do it is to connect (only) the winding CT to the elevated reference.

Remember, the point of DC heaters is to maintain a zero AC signal condition between the heaters and cathodes.

With what you describe, the current through the heaters will be DC, but I believe that the voltage reference between the heaters and cathodes will be fluctuating at 60 (or 120?) hz.

If you go this route, you could try adding a 10,000uf cap from DC 0v to ground. I always think that this should make smoke, but it seems to work.

[Jana]

You're making this way more complicated than it needs to be. If you just want to experiment, fine. But, if you are going for reliability, there are a lot of extra parts with this design. If the goal is to reduce hum, then concentrate on good layout and lead dress. It's possible to build high gain amps with 4 gain stages in the preamp and use plain old 6.3 VAC for the heaters and not have any hum.

[oldmacman]

You're making this way more complicated than it needs to be. If you just want to experiment, fine. But, if you are going for reliability, there are a lot of extra parts with this design. If the goal is to reduce hum, then concentrate on good layout and lead dress. It's possible to build high gain amps with 4 gain stages in the preamp and use plain old 6.3 VAC for the heaters and not have any hum.

Agreed. For anything with humbucking filaments (e.g. 12A*7), you should be just fine with AC filaments. You really only need DC with tubes like 6SL7 where a significant amount of hum does get coupled in via the cathode. Dumbles and Trainwrecks have plenty of gain and don't hum, and they use AC filaments.

[oldmacman]

In reply to oldmacman:

In reply to structo:

I think it does need a "0" reference point. I think the best way to do it is to connect (only) the winding CT to the elevated reference.

If you go this route, use two 100 ohm 1 watt resistors to create a "virtual" center tap which you can connect to ground (or to your bias supply or a divided-down positive reference voltage to further reduce hum), and leave the heater center tap disconnected. See http://www.drtube.com/schematics/marshall/4001m88.gif for an example.