Submini question - tis the season!

[zombie_rock123]

With all the submini projects in the Beanpipe I thought Id have a go at breadboarding something. I put together a subcaster, tacked on another 6N16 tube, added a tone stack. I was thinking that I could just run the heaters in series to avoid buying a 317, 6v reg or huge resistor. 12 volts / 2, job done, also works fine for the plates.

Sounds amazing, really love these little things but I think I might have an issue. My PSU is 12v 1.5A and when I've measured the heaters I'm getting less than 6volts on each, round about 5.5, and from my googling before I started in this topic someone mentions that series-ing them isn't that good as 6 is the absolute minimum:

http://www.diystompboxes.com/smfforum/index.php?topic=66746.40

So my question is, do I not care about the voltage difference, or do I hook them up a different way? The only way I can think is to power it with an 18 volt PSU with a 12 volt reg for the heaters. But this seems overkill really.

Typing all of this out I have realised that I have no filtering yet - no small value/large watt resistor to separate the power for the plates from the heaters. If this is my problem then I feel like a jackass. But still wondering if that isn't likely to be the issue Still trying to get a handle on the whole regulator/massive resistor thingy and series-ing them seemed to be too good to be true!

[Scruffie]

If you're happy with the sound, I wouldn't worry. Under voltage is a lot better than over voltage, the Valvecaster uses a 12AU7 at 9V instead of 12V for the heaters, it just means the tube isn't going to be running to the datasheet specs with the added benefit it might live a bit longer.

IIRC the 6N16 is 6V+/-300mV anyway so 5.5V isn't that far off and as you say, going for 18V (or having them in parallel with a 6V regulator from the 12V supply) is a bit overkill and adds its own headaches.

[madbean]

Yeah, I agree: if you like the sound that's what matters. I have found in some cases that 6.3v vs. 6v can make a big difference (surprisingly) but only with a single tube. With two heaters in series maybe it's different, or maybe that was just a special case.

[zombie_rock123]

Awesome, thanks for the reassurance and info guys!

The big-assed resistor usually seen on these things - I'm guessing it's usually to drop the 9/12/18 volts to 6 for the heaters, but in the Subcaster there's a (presumably) big wattage/low value resistor for the supply to the plates. If you don't need the 6 volts for the heaters is it just a case of using a small value honkin great resistor for filtering given the amount of juice it's going to draw? I can't believe I'm actually going to have a use for a sub-10R 5 watt resistor...

[Scruffie]

Ohm's law.

It's all about current draw and voltage drop, the heaters draw a LOT of current so if you wanna drop the voltage down 6V, you're going to need a hefty wattage resistor to stop it frying. For the filtering, a larger value resistor can be a smaller wattage but will drop more voltage, the plates don't draw a huge amount though, a few mA but it depends on your supply.