Effects between amp and speaker

I have heard people talking about putting time-based effects (delay, tremolo, etc.) in between the amp itself and the speaker cabinet. Has anyone ever heard of doing this or is it even safe? The THD Hotplate (which is placed between the amp and speaker) has a Line OUT, but I believe it has to go to another power amp to be used. I'm trying to exhaust every avenue of my sound, looking for something that is my own..... I haven't found it yet.

Another similar question: Is there any way to simulate an effects loop for an amp which does not have one?

OUT, but I believe it has to go to another power amp to be used.

Correct. Use any power attenuator as a dummy load; use the dummy load component that's in any power attenuator, and leave the load-splitting circuit unused.
is my own.

Eddie Van Halen made the 3-stage amp rig his own sound, and also split the signal after the dummy load, to form one dry guitar speaker cab and one for late fx such as reverb.

Trent Reznor made the fake-o degraded simulator processor sound his own, playing on its signature artificial and cold character.

Start by not innovating, but use either of the two standard professional studio rig chains: 2-stage amp rig with power attenuator, or 3-stage amp rig with dummy load:

Standard 2-stage amp rig with power attenuator:

eq and other fx (stage 1)
preamp distortion (pedal or amp's built-in)
eq and other fx (stage 2)
tube power amp power attenuator (as loud as permitted)
guitar speaker, pushed hard, possibly in an isolation booth or iso cab multiple mics mixer eq and other fx (stage 3)
monitor speakers or headphones

Standard 3-stage amp rig with dummy load:

eq and other fx (stage 1)
preamp distortion (pedal or amp's built-in)
eq and other fx (stage 2)
tube power amp dummy load (can use any power atten's dummy load)
eq and other fx (stage 3)
power amp (solid-state is fine here)
guitar speaker, pushed hard, possibly in an isolation booth or iso cab multiple mics mixer eq and other fx (stage 4)
monitor speakers or headphones have one?

Turn off the amp's built-in preamp distortion, and use a distortion pedal instead:

[effects group 1] distortion pedal [effects group 2; equivalent to fx in amp's fx loop] amp's input jack amp's built-in preamp distortion not used amp's tone stack tube power amp guitar speaker

This posting contains all the most important basics that the guitar gods know, but that every beginning guitarist should be immediately taught on the first day, with their first A-shaped power chord. Study it as the gospel of
Tone victory and entry into the kingdom of Tone heaven. Guitar-god Tone is also in the crazy fingers which are inspired by pot and acid.

The only effect you will get out of running an effect between the amp and speaker is called PYRO!!!..A fog machine is cheaper.
Not meaning to be ugly,and I am not trying to be,but do you own gear,or are you just doing research for a school report or project.You should have known better than that..Maybe it is time to put the pedals and ideas up and just practice,then you will be able to get out and jam with other people and learn things from them first hand.Don't give up the ship because the water is a little choppy..Take care.

I suppose the phrase, "The only difference between knowing, and not knowing, is knowing" applies here. Wasn't there a point where you didn't know?

Generally speaking, you CANNOT simply put effects between the amp and the speaker. The signal levels are entirely different from an effects loop arrangement.

With your hotplate, you can run the line out through some effects, then into a *separate* power amp, and then to your cab.

While I won't swear there isn't one, I know of no way to "simulate" an effects loop without using the arrangement above, i.e., separate power amp.
It is often possible to have an effects loop installed, but I wouldn't do it on a vintage amp. Also, make sure you get someone who really nows what they're doing. It's not a complicated mod, but it seems to be executed poorly fairly often, from what I've heard.