Damage to Head when not connected

[ToneZone]

I've heard that ampheads can be damaged by using them without a cab?
Is this true?
I have a marshall JVM 410H that I was thinking about running straight into my Line 6 toneport and let either the line 6 gear or NI Guitar Rig do a cab sim.
Any idea if this might work?

[bucketbrian45]

Almost every Marshall I have seen says on the back not to turn it on unless it has a speaker load connected to it.

[ToneZone]

Do you know why? What happens?
Perhaps it time to ask the support... :P

[Robert Burns]

On ebay you can get just 3" long 1/4" "Adapters"...that provide a speraker
load, without the cable. Its real bad on the transformer, to have such
high voltage, and no load on it. Blows Caps too i think?

[Rsmacker]

I've no idea about your setup, whether you can use it as a power soak or dummy load, but in general, with valve amps, running them without a speaker attached is a silly idea. It fucks your output transformer for starters, and will cost you a pretty penny to repair.

[Hellbat]

I've heard that ampheads can be damaged by using them without a cab? YES
Is this true? YES
I have a marshall JVM 410H that I was thinking about running straight into my Line 6 toneport and let either the line 6 gear or NI Guitar Rig do a cab sim.
Any idea if this might work? YES - IT WON'T

Not only will you likely damage your amplifier, you stand a good job of nuking your toneport and possibly computer at the same time.

You want a speaker simulator type device that plugs into the head and gives you a line out signal. Something line this....

http://www.groovetubes.com/SEII_Speaker_Emulator_P1604.cfm

The voltage output from the power amp section to a speaker is much higher the than the line or instrument level output the toneport is made for. They are looking at less than 1V peak to peak at very low currents. A 100W amp is capable of putting out much larger voltages and currents. So the amp will eat itself while also killing your other equipment.

[DonP]

I've heard that ampheads can be damaged by using them without a cab?
Is this true?
I have a marshall JVM 410H that I was thinking about running straight into my Line 6 toneport and let either the line 6 gear or NI Guitar Rig do a cab sim.
Any idea if this might work?

What everyone else said.

You will be looking at a very expensive repair bill.

[ToneZone]

Ah.. So none of that.
Time to get a good cab.

Thanks everyone for your help.

[Matt_B]

I have a marshall JVM 410H that I was thinking about running straight into my Line 6 toneport and let either the line 6 gear or NI Guitar Rig do a cab sim.

They only reply I can give about this sentence is:
- Instrument level
- Line level
- Speaker level

Learn about them before you blow something up.

[lerxstcat]

Do you know why? What happens?
Perhaps it time to ask the support... :P

Whenever this question is asked and the above post is the folllowup, I always imagine the guy deciding he's gonna hook it up until someone gives him a reason that's acceptable to him - or for the short time it takes to blow up his amp, Toneport, and computer! I hope this didn't happen this time!

Have seen the same thing with someone using a guitar cable instead of a speaker cable to run from the head to the cabinet. If it hasn't damaged the amp YET (IOW, they're LUCKY), they ask, get the answer, then want to argue about it.