Newbie! Running a tube cold!

[ioginy]

I have an idea for a circuit that would need to use a pre-amp tube running just below working temperature. Almost like it is half prepped so when it is given power it would roll into functioning temperature immediately instead of taking 10 seconds like a tube amp would normally take at start up.

I have no electronics training, so I don't even know if this is possible. I have been doing a lot of reading and haven't found any reason why it wouldn't work, but I thought it would be a good idea to ask around.

If anyone can help me with this it would be much appreciated. If this can work, it will make a dream of mine come true.

[Enzo]

If you mean in something like a preamp? or building a pedal?

If you mean have the heaters on but not all the way hot, we would call that a preheat. Stage lighting uses the concept.

SInce preamp tubes can last 30 years, why bother? Just leave the heater running. If it is an energy thing, the difference in preheat levels and all the way on would not be a lot.

No, there is no particular reason it wouldn't work.

[d95err]

I suppose an ordinary standby switch wouldn't work then?

If you want the tubes to be in standby-mode but slightly below operating temperature, you can use a double-pole standby switch. One pole as the ordinary standby, and the other inserts a high-current capacity diode in series with the heater winding. This means the heater will operate at half voltage/current and the tubes will run cooler. Once you switch out the diode, the tubes will reach operating temperature quickly.

[Don Moose]

It _is_ possible.

It is pretty pointless, though.

For maximum tube life, you want the tubes to be fully warmed up before any other voltage is applied (see Cathode Stripping). A power supply sequencer to guarantee the order voltages go up (and down) is a pretty complicated thing.

I remember asking around here if heating tubes externally would work (no). Still it was fun to think about.

[Jag]

I remember asking around here if heating tubes externally would work

LOL. I had visions of a monster amp with several blow torches mounted to the back.

[David Schwab]

I remember asking around here if heating tubes externally would work (no).

It's not just the heat, it's the electrons that flow from the hot filament (cathode) to the cold plate (anode).

[ioginy]

Well, my reasoning is for a pedal. What i want to do is build a pedal that uses the warm up up a tube to create a roll in for the effect instead of having it just turn on and off. Having a tube warmed but not functional to give about a second of build after the pedal has been engaged is the only way I could think of doing it.
Someone told me I could do it with capacitors as well, but I researched them on that respect and as far as I can tell they just work like a bottle of water over flowing, which is not what I am after.

I'm fairly layman when it comes to technical info.

[cminor9]

Well, my reasoning is for a pedal. What i want to do is build a pedal that uses the warm up up a tube to create a roll in for the effect instead of having it just turn on and off.

*shrugs* Maybe you are approaching the problem from the wrong vector. Maybe put a volume pedal in before the effect? That would give you sort of a fade in.

Heck, you could pretty easily build one that, when off, bypasses your effect but when turned on goes through the effect sort of like a volume + A/B. Then you'd *have* to turn it up to use the effect. Then it's just a matter of how quickly you roll up the volume. Get an old/cheap wah pedal and use the housing, pot, and switch for it. Toe it to turn the effect on (defined as short circuiting the bypass), and then heel it up to turn up the volume (thus the effect). Toe it again to turn it down and click to enable the bypass again when you are done with the effect.

That way you get your tube on all the time and avoid cathode stripping, get your gradual-on feature, and a cool project to boot. Plus, this would give you more control over how fast the effect ramps up than with just letting the tube heat up, which could vary from tube to tube. I guess as another bonus you could use this with any other effect(s) or as just a standalone volume pedal. Now that's multipurpose!

Just an idea. I have hacked wah pedals for other things. They seem to be a good platform to work from.