Running a Valve Amp With no Speakers

[bails]

I've heard bad things about running an amp with no speaker connected. I've also heard people refer to a lack of speaker as "no load" even though it's actually the complete opposite - no speaker equates to an infinite load, because there it becomes an open circuit.

From my limited knowledge of electronics, I can see that when the impedance is lowered, more current flows through the wires, causing excess heat, and the obvious problems of melting, shorting and fire. For this reason, running a valve amp with the output impedance set at a higher value than the actual load is very bad...

Using the same principle, increasing the load, actually reduces the current flow, making the output transformer run cold. Now while this may not achieve a necessarily great sound, running a transformer cooler than it is supposed to run isn't going to damage it, so what's the big problem?

As far as I can see, running a amp with an infinite load (no speaker) is] safer, and much less hassle than fiddling around with dummy resistor loads (which I have been told should always be installed in lieu of a speaker).

Am I missing something?

[ozover50]

Back in the 70s and 80s when I had Quad, Macintosh and Lafayette valve stereo amps, no speakers was a huge no no!! The same thing with the Goldentone and Eminar guitar amps I owned. I never saw it happen but I heard horror stories of amps smoking themselves when speakers weren't connected. Things are probably different these days, however.

[admin]

Mark: It may be less of a hassle but in my view you will ruin your amplifier. An alternative would be to get a THD Hot Plate or one of Ted Weber's attenuators.

[jps]

Tube amps need a speaker load, do not run one without it or a dummy load (resistor). AFAIK, attenuators such as the Hotplate are not a substitute for a speaker load, you still need the speaker or resistor in place. You WILL have a meltdown if you don't heed this.

[fatcat]

Using the same principle, increasing the load, actually reduces the current flow, making the output transformer run cold. Now while this may not achieve a necessarily great sound, running a transformer cooler than it is supposed to run isn't going to damage it, so what's the big problem?

That only stops the current in the transformer's secondary, the primary is still conducting, and now has to dissipate the extra power that it can't transfer to the correct load.Instead of sound, the energy becomes heat, and then smoke.

As far as I can see, running a amp with an infinite load (no speaker) is] safer, and much less hassle than fiddling around with dummy resistor loads (which I have been told should always be installed in lieu of a speaker).

Am I missing something?

Yes. Just disconnecting the load does not stop the amp from producing power, which must dissipate,as sound ,or heat.

[jingle_jangle]

Transistor amps need a speaker load, too. Every manual I've seen says so, although I suppose there are lots of poorly-written manuals that fail to warn.

[soundmasterg]

You can in some situations safely run a tube amp without a load, but ONLY when you don't have any signal going through it. Personally I don't ever do it though as the risk is there to cause damage. Just use a load....even dummy resistors are cheap. You can get a 100 watt 8 ohm power resistor at a surplus place for $10 or so, maybe even less.

Greg

[headbanger]

Hey Howard, you had/have an Eminar too? Awesome Aussie made amps!
I once ran mine without the speakers plugged in by accident... I kept turning it up whilst saying "what's wrong with this thing". It got to the point where I could here the tubes rattling..... Oops.
It didn't do any damage and it wasn't for long.

[beatlefreak]

Always run a power amp circuit with a load connected. As previously stated, the power generated has to go somewhere - What doesn't come out as sound energy dissapates as heat. Heat destroys electronic circuits (or at least shortens their life).

[ozover50]

Hi Gerry! Yep! I had an Eminar 100 watt bass amp..... and bloody good (and heavy) it was, too! I also had an an Eminar PA amp. They still pop up on ebay every now and then.

[headbanger]

Howard, I've had two. A 50w bass head and the 150w monster I have now. A friend has a 120w PA head. Great robust tube power amps. Oz eq to a marshall/ampeg.

[rictified]

Tube amp + no speaker = Big Bucks.