Power up with no speaker connected?

[Tdale]

This will destroy the amp, right?

I'm always a little concerned when people borrow my amp. What if they don't know that you shouldn't remove the speaker jack when the amp in switched on? Or what if the jack plug falls out?

Is it possible to use a closing jack, and put a 8 ohm resistor there, so that when the speaker jack plug is removed, the 8 ohm resistor connects, giving the OT a load?

Tommy

[d95err]

This will destroy the amp, right?
Is it possible to use a closing jack, and put a 8 ohm resistor there, so that when the speaker jack plug is removed, the 8 ohm resistor connects, giving the OT a load?

Tommy

Yes it works - as long as the resistor can take the power.

I've got this on a small amp I built. It puts out about 15W clean, so I used a 50W power resistor with a built-in heatsink. I bolted it to the chassis with some heat conducting silicon paste in between.

I use it with a line out, so I can record silently at home. The resistor and heatsink get extremely hot after a while when I crank the amp. To be safe, the resistor needs to have a power rating of at least twice that of the amp. For a 50W or 100W, you would probably need extra heatsinks and a cooling fan.

Note that the high power resistors are only needed if you really want to play the amp with no speaker (i.e. using some kind of line out). If you just want some protection for the "why is there no sound - oups I forgot to plug in the speaker" case, a common solution is to put a small power resistor across the OT secondary. Approximately 200 ohms 5W should work. This will protect the OT for a short time, but will not stand up to continous playing without a speaker.

[Tdale]

A short time as in a few seconds, or a couple of minutes?

Tommy

[Luthierwnc]

It takes at least a few minutes. They have to get hot before they smoke. Put a piece of duct tape across the sucker that says, "Lethal voltages" or "you break, you guy" on it.

Is the guy an air guitarist?

sh

[Funkalicousgroove]

As long as there is no signal going through the amplifier turning it on with no load won't hurt it. Now, once you put a signal through it watch out for 3 mile island!!! You'll hear a faint whistiling sound of what you're playing-then SMOKE!!!!!!!!!