Modding a charge pump from 18V to 12V output

[midwayfair]

Who said anything about wasting 6V at 300mA? Even his original plan was to waste 3V at 300mA which is perfectly doable really, the 7806 is fine up to 1A but of course does need heat syncing.

Sorry, I thought he was asking about using an 18V supply and dropping it to 12V.

And I meant without a heatsink re the 6V drop if he'd been using an 18V to knock it down to 12V.

>Problems running it at 9V

A single 12V supply does everything you need as long as the one you get can supply the current required for the heaters and still have some leftover mA. It's pretty much ideal for the circuit since you don't need any regulation and it'll run sound through the tubes.

A 12AU7 doesn't require as much voltage as a 12AX7 and will absolutely sound way better, but a 12AU7 might still just a bandaid if you have a problem with the sound of a low plate voltage tube circuit. If you're building a starved plate design instead of using a voltage multiplier circuit to get full plate voltages of whatever triode you want to use (i.e. not just a voltage doubler or tripler to get ~22-32V from an LT1054), then I think it's just easier to embrace the fact that it's a starved plate and say, "Well, that's what the valvecaster sounds like." Most of the problems you were reading about with the 9V circuit probably had to do with powering the heaters.

There are other types of voltage multipliers you can build if you want to make something in the future with full plate voltage. Like I said, GrindCustoms has one. (And if you want to get really fancy, theirs can also be modified to run on a dedicated 12V adapter to avoid regulating the heaters down to 6V.)

[MarkL]

So Scruffie and Jon...do you think it would be more advisable to power this with a charge pump changing 9V into 12V, or would it be better to power it with a 12V wall wart? 

(and if the charge pump is okay, could I then just use the Road Rage and modify the regular to an LM78L12 or something else like it?)

The reason I ask is because if there isn't that much of a difference, I'd rather just be able to power the effect from the powr supply I use for most of my 9V pedals (a Dunlop DC Power Brick) because then I don't need to worry about carrying a separate wall wart.

[MarkL]

Actually, Scruffie, I looked at the Road Rage at it puts out a maximum current of 100mA.  If I understand the Valvecaster-type devices correctly, they require more than that...about 300-500mA or so, or more.  If you think using a RR-type charge pump will sufficiently power the circuit at 12V, why is there such concern that the circuit be run at 300-500mA?

[Scruffie]

I think I can speak for Jon and my self here when we say use a dedicated 12V DC supply for the heaters, once again, a charge pump cannot deliver the 150mA required for that job.

If you wish to use a charge pump to power the plates at a higher voltage however, that is up to you.

I say 24V vs 12V on the plates will make a noticeable difference (far more than the same change would make on an opamp) so using a charge pump (the tubes heaters will still be powered directly from the 12V dedicated wall wart) on the plates is worthwhile for a bit of extra oomph.
Jon is suggesting either just powering both the heaters and plates off the 12V supply and forgetting the charge pump or using an SMPS (think of an SMPS as a sports car instead of a charge pump being the family hatch back) which can provide 100-200V+ to the plates to get the best out of the tube but they are far more finicky than charge pumps, require specific parts choices and can give you a nasty electric shock, i'd save that for later builds when you've gotten some more experience in tube circuits.

[blearyeyes]

The power supply rating of 100ma is not about the power supply limiting it's output to 100ma. The rating of 100ma is the maximum the power supply can provide the circuit. if the circuit "Draws" too much power, more than the power supplies rating, your transformer will be pushed to provide more than it's designed rating, or the circuit will suck too much juice and could smoke the power supply.

Hope this helps.

I know you probably already understand this...

[Scruffie]

Actually, Scruffie, I looked at the Road Rage at it puts out a maximum current of 100mA.  If I understand the Valvecaster-type devices correctly, they require more than that...about 300-500mA or so, or more.  If you think using a RR-type charge pump will sufficiently power the circuit at 12V, why is there such concern that the circuit be run at 300-500mA?

The Road Rage can actually only supply 50mA.

Anyway, I think I see where the confusion is coming from, vastly over simplifying it, a 12A"7 tube has 2 sections, the first section it has are the heaters which turn the tube 'on' these can be run from either 6V at 300mA or 12V at 150mA, they are a separate part of the circuit to everything else.

The second part of the tube is the bit where all the audio stuff happens, this is where the plate (or anode) lives which can take voltages up in to several hundred volts and only draws a small amount of current so that bit can be powered by a charge pump.

Jon is better at analogies than me so he can probably describe it better.

[MarkL]

Actually, I think I know really do understand what's going on here. With all of the different options, and the fact that I want to use this as an overdrive rather than as a boost, I think simply powering the entire circuit (both plates and heaters) at 12 V from a wall wart will be the best option.

Now -- anybody have any suggestions for a preferred 12v DC wall wart to use with this thing?  :-)