2 amplifiers connected to 1 set of speakers

I had a speaker cable from a tube (valve) amp fall onto a cable plugged into a class d amp. It was biamped. The weird thing, the class Ds were not ON, just plugged in. That cable drop tripped a 20 amp breaker, took out a channel on my MC275 GG and a second VTL 300 MB. 
I had to laugh, what a fumble. I'd have never thought a cable could cost 2500.00 in repairs. Not long after, my main preamp a C2500, lost the right channel.  Coincidence, I don't think so.. I have all my gear hooked to cleaners and maintainers. NOT a single blown fuse, or tripped breaker, only at the main when it first happened...

Be careful.. 50+ years of this. I never pulled one like that....

Regards

Well, there is biamping.
Either Vertical or Horizontal, but you would be sending a signal from each amplifier to a different set of speaker terminations-for speakers wired for such.
B

Instead of swapping cables, I think using a high quality amplifier selector is a safer way to switching amplifiers.

http://www.beresford.me/S/home_htm_files/TC-7220MKII.pdf

To be clear. I have two amps, two pair of speaker cables, one pair of speakers. I’m not asking if it can be done or how it can be done, I’m asking what would happen if someone tried. Thanks for the responses thus far.

POP a fuse if your lucky, if not it's all down hill from there, from a pop to a BOOM, get my drift? 
There is a way to combine amps if they are made for it, "strapping" or "bridging". You bridge the amps, then run a single set of speaker cables if you have a single set of speaker binding post. A lot of pro/car audio stuff is that way.  Mcintosh, too, they can be strapped and stacked..
Grateful Dead, used 2300 or 2500, maybe both.

You want an A/B switch... be careful.. Don't switch live.  It will be in the signal path. Something to think about.. A cheap switch box, maybe not a great idea for quality sound...

A good passive preamp.. good traces, good wire, good switches.. 100.00 and you can fiddle a bit. Still in the path though...

Regards

She asked me why it wouldn’t be ok and I started babbling that the signal from one amp would then travel through the other set of connected cables into the amp that was not in use. Even if the other amp was off that could be problematic. If the other amp happened to be on then it could prove catastrophic for both amps and potentially cause an electrical fire.

What is the correct answer fellow audiogon members? Ralph?

The correct answer to your wife’s question is of course:

"Good question, honey. Now all I need is a new set of cables...!"

Most (not all) SS amplifier has relay at the output for delay turn-on and protection. If both tube amp and SS amp are connected to the speaker and only the tube amp is on, it will do no harm to both amp because the SS amp output stage is disconnected by its built-in relay.
When the SS amp is on and the tube amp is off, then the SS amp will see the speaker as a load and also the tube amp output transformer secondary winding parallel to it. That will be bad for both amplifiers, there’s possibility fries the tube amp OPT and damage the SS amp or put it into protection mode.
Even though if the tube amp OPT secondary winding strong enough to stand the current from the SS amp, the speaker will definitely sounded weak with no bass because the inductance of the OPT secondary winding drained all bass energy through it.

Good answer. Impressive, even.

I would however want to be ready with the follow-up, "But what if they're both on?"  

ghasley,

I know you are just raising a hypothetical question of what would happen. However, since you seem to have occasion to swap amps, you might find it more convenient to do as imhififan suggested and get yourself a Beresford Switch. They make several kinds. I have one specifically made to swap between my tubed mono blocks and my SS amp to a single pair of speakers. Just make sure amps are off when to throw the selector switch.

J.Chip

Hmmm, she may be thinking it’s time to ‘downsize or declutter’. Proceed with caution or an ‘I don’t know’

@b_limo

That is one of the few units I custom built for my friend to demo amplifiers in his shop for his customers and his audio club.
His customers usually don't had time to wait an hours or two for setting up and compare tube amps, so these selectors can switch between amps, while one amp is playing the other amp still on with dummy load connected, it is the best compromise we can think of.

No offense intended to anyone but Im not looking for a way to switch between the amps. It isnt hard to switch cables at the speakers. I have two sets of transparent gen5 speaker cables, one optimized for the tube amp and one for the solid state. Im looking for an educated explanation of what would happen. Sparks, blown caps, transformers? I appreciate @oldhvymec explaining what happened. Other explanations welcome but im not looking for a switch. Peace and thanks. 

The cables have different inductor values, and maybe a little different HF inline XO.  Yup, Snap, Crackle, POP,  just like the cereal.  ;-)

Do the Douglas Fargo on Eureka. LOL...

Regards

I thought the first post covered it? 
I borrowed a carver sunfire amp that survived such a experiment when I wired both channels into 1 speaker, but I wouldn't deliberately wire 2 amps to the same pair of binding posts unless I was looking for an excuse to go out and replace everything.

no

What is the correct answer fellow audiogon members? Ralph?

The correct and short answer is no.

If you really want to do this you could use a switch, but often the switch messes up the sound.

Thanks @atmasphere 

To be clear, I do NOT want to do this, I was wondering what would happen if someone did. I am perfectly content to disconnect the speaker cables at the speaker when I want to switch amps.

What happens is the output section of one amp loads the other. This is bad when one is off, worse when both are on! Smoke and other things happen!

DON'T DO IT!
I've done this.  A long time ago.  Twice.  With two receivers.  First, by accident.  Second, purposely.  
There are conditions that may allow you to do so with no harm.  As long as both are NOT ON at the same time.  But without diving into the circuitry with a schematic, one will not know.

The details are clouded but here's the best I can remember.
The first thing I notice is the system will not play as loud.  One usually knows how loud their system plays at say the 9:00 position. (btw this was enough to kill the other amplifier)  But going on.  So, you turn up the volume to 1-2:00 position to achieve the correct volume. Why?  I figured that I was feeding power to my speakers as well as backwards into the other connected amplifier.  Which it's output devices did not like.

The first time noticing something was not right (the 9:00 position), I just wiped out the 4 output transistors of the Connected Receiver.
The second time I went for the 1-2:00 push.  And then turned the Connected receiver ON.  OH  BOY.  A loud burp from the speakers.  Flashes.  Smoke.  It blew just about all the fuses and the outputs transistors of both receivers.  Plus the driver circuit board to the output transistors of the Connected receiver.  Quite exciting.  And destructive. 

DON"T DO IT.

Ghasly, your answer in your original post is the correct one and the best answer here. Both amps will be connected to each other and bad things will happen. Even when they are not both turned on. Keep doing it the way you are now and nothing bad can happen.