Why are most tube based pedals running on low voltage.

[lightningfingers]

I've built the real McTube, so has Paul Marossy, theres an article on his site about it.
Mine sounds great with a Mullard 12AU7, but hums and oscillates a little when bypassed (I built another one with shielded cable which seemed to solve the problem)

[davebungo]

Valves generally run off HT supplies but the heater supply is always taken from a separate winding on the power supply transformer.  The specs for ECC83 are nominally 6V DC or AC for the heater supply voltage - current will be a few hundred mA.

[Paul Marossy]

As pointed out, I built the Real McTube. The problem with the Real McTube is that you can't fit it into a Hammond 1590BB enclosure like you could with the Shaka Tube or the Tube Driver. So, if that's not a problem, it's a good sounding circuit. It's also different in the fact that it operates on about 140V plate voltage instead of around 30V in the aforementioned circuits...  

[barret77]

Hey, you have put a Mullard into the pedal - it should sound really good... those are famous in the tube amp world

[Doug_H]

It wouldn't have anything to do with reduced headroom would it? I'm not that knowledgable about tubes and amp design but wouldn't you do everything you could to push them into breakup? (Or is the pedal you mentioned a clean booster type overdrive?) Doesn't reducing the voltage reduce the headroom?

Well, if you are talking about a low voltage "starved-plate" circuit (where a typical high-voltage tube is run at a low plate voltage), you will notice that the tube stages are usually run at low gain too. The BKButler Tube Driver operates this way. So while the supply voltage is much lower than for a normal operating point, the gain is scaled down too, which helps with the headroom.

There's a good article at the Paia site that explains the "space charge" phenomenon when plate voltages are starved.

Doug

[ninoman123]

Ive heard the tube driver is a bit noisy...well it was posted somewhere. Would this be the builders fault or is it the way of the circuit?

And the noob question of the day...what is shielded wire? Anyone got a picture of it? Where can I get it. I should prolly check SBE before I say that....lol... :oops: