Guitar amp switching

moamps said:

It's loaded with another speaker.

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OK.

just build a zero crossing detector, 

actually, this whole hot swapping thing has been around a while,

a lot of technology involved when you start bringing hoover dam online,  so it is just a matter of how involved you want to get as opposed to buying two more amps and two more speaker cabs and switching them from the input jacks.

Good Lordy, how would you like to swap RF tubes, no thanks!

"Modern day radio transmitters (and some TV transmitters as well) use high power RF transistor power modules instead of vacuum tubes. Hot swapping power modules is not a new technology, as many of the radio transmitters manufactured in the 1930s were capable of having power tubes swapped out while the transmitter was running—but this feature was not universally adopted due to the introduction of more reliable high power tubes."

abbey road d enfer said:

See attached schemo.
There's only one point to take in consideration; with both amps off or both on, their outputs are connected together. The risk of damage  is not considerable, but if you want to avoid it, you have two possibilities:
1) Be very cautious
2) Use interlocking switches; I would recommend that. The best interlocking switch is a rotary switch IMO.

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Thank you sir

Now I see what you mean... thanks again

Best regards

/ John

moamps said:

Dummy load isn't needed at all if only one amplifier works at a time (another one is muted at input).

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Thank you sir

That is genius...

Best regards

/ John

Switching speakers while the amps are cranked and delivering signal  ;D    Flash bang wallop:-[ 
a re-think or re-jig of what your trying to  achieve  might be the best approach. 

Thanks for clarifying those points Abbey, 

Flash bang wallop

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The trick is to not play while changing the speaker hook up.  Having a mute input with millisecond delay before the speaker switch, can force that issue.  If your the one controlling the switch then you train yourself to not play when switching speakers.  If this is for some bonehead guitar player,  than all bets are off.  BTW all guitar players are boneheads at one time or another.  As a guitar player I can vouch for that.     

fazer said:

The trick is to not play while changing the speaker hook up.  Having a mute input with millisecond delay before the speaker switch, can force that issue.

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Even without signal, a tube amp can blow up when disconnected from the load, contrary to solid-state amps.
In most cases, it would withstand a momentary disconnection, such as the time it takes a switch or relay to changeover.

There are some commercial units that do this,  but  from the externals it doesn't seem like they are using high wattage loads.

But if you mute the amp input how much power will you really see at the output?

you can put flyback diodes on the opt plus the 620 resistors on the jacks and breathe easy,

has this been mentioned already?

CJ said:

you can put flyback diodes on the opt plus the 620 resistors on the jacks and breathe easy,

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Why 620? I would think you would still want something close to what a speaker would be.

john12ax7 said:

There are some commercial units that do this,  but  from the externals it doesn't seem like they are using high wattage loads.

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If actually switching from one cab to another, a dummy load is not necessary because the amp can withstand being unloaded for a short duration. The changeover time of mechanical switches is in the order of a few milliseconds, which is usually not long enough to do actual damage.

But if you mute the amp input how much power will you really see at the output?

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That is correct; if everything goes according to plan, a 1/4W resistor should be enough to maintain stability of an otherwise unloaded amp. But in real life it happens that the amp is not muted and the guitar hero slams a big fat E chord.