MAX1044, low voltage tubes, and power supply sag

[balance]

With all of the talk here recently about the 12au7 and low voltage tube boosters, I've been considering something similar for my next build.

I'm sure this has been considered before which is why I am tabling it here. Someone will save me a lot of work by simple saying, "Nope, ain't gonna work."

The idea would be to run the tube's heaters in series at 12.6 VAC (or there about), then rectify/regulate back down to 9 VDC with a 7809. Finally, I would use the charge pump (MAX1044) to get the voltage up to somewhere between 17 and 25 VDC (a la "One 9V battery gives +18, +25, +33V" from R.G.'s geofex.)

If I understand the MAX1044 datasheet correctly, when the load current increases, the voltage drops. I was hoping that this would simulate the "sag" that is common in tube amp power supplies. The current requirements of the 12au7 are not immense, and a drop of only a few volts should be noticeable. What will probably be more noticeable is the noise created by the added ripple.

So, how far off of the mark am I? I'm not totally a noob to pedal building, but I am certainly not an EE.

Anyone?

Brian

[Renegadrian]

will the max1044 accept 12V on input? If so, it'd be possible to double it and get 24V?!

[frequencycentral]

Yeah, I am doing something similar - see this post: http://www.diystompboxes.com/smfforum/index.php?topic=69886.0

And this one: http://www.diystompboxes.com/smfforum/index.php?topic=69738.0

I'm using a MAX1044 running at 12 volts (bad practice!) to achieve plate voltages of up to 44 volts. I'm still experimenting, but tube are definately more symettrical at these voltages.

You should, however, try the LT1054S, which is similar to the MAX1044, but it will run on 12 volts, whereas the MAX1044 is only recommended up to 10.5 volts. It also has a high ma output 100ma compared to the MAX1044's 10ma.

I am having good results - but I'm still prototyping. It would be good to have someone to compare notes with.

[R.G.]

The idea would be to run the tube's heaters in series at 12.6 VAC (or there about), then rectify/regulate back down to 9 VDC with a 7809. Finally, I would use the charge pump (MAX1044) to get the voltage up to somewhere between 17 and 25 VDC (a la "One 9V battery gives +18, +25, +33V" from R.G.'s geofex.)

If I understand the MAX1044 datasheet correctly, when the load current increases, the voltage drops. I was hoping that this would simulate the "sag" that is common in tube amp power supplies. The current requirements of the 12au7 are not immense, and a drop of only a few volts should be noticeable. What will probably be more noticeable is the noise created by the added ripple.

Thoughts in no particular order:
- If you're going to use an AC power supply for the heaters at 12V, it's pretty simple to just use the pre-existing AC and a doubler/tripler/etc to get 30/45/60Vdc. The hard part about making higher voltage DC with a multiplier is getting it to be AC first. You already have AC.
- Rectify/filter/regulate to 9V, then up-vert in a 1044 is sure a lot of work and complexity.
- the 1044 is a poor choice if you don't already have a 9V limited DC supply to run it from. The LT1054 is better, tougher, higher voltage and current.
- You can always put sag back in - just insert a resistor in series with the power supply. You don't have to use a concoction of ICs which inherent sag. Resistors work as well.

[Renegadrian]

Let's make a case...

a) power from a wall wart, 12v, 300ma or more (I've got a 500 too and a couple of 1M)
b) at least 150ma are for the tube heaters.

Apart from the heaters ma needs, how many ma are taken by the rest of the tipical tube construction, as seen to say in our Valvecasters? Will those lil' 10ma be enough for it?