The thing about not grounding the load is pretty much specific to amps that use current feedback and amps that operate in 'bridged' configuration.
This one is probably not either, but no harm in moving the scope ground to chassis, that is usually the best place for it anyway.
Any time you see a heatsink or a high power resistor, expect heat.  So I expect that TR201 to get hot.
In older stuff, they did not have dedicated voltage regulators so they used regular power transistors in a regulation circuit (often 'pass transistor' topology).
Check the DC readings on it's pins, that may give an idea of what it is doing.
You may be in for a bit of a rodeo with this one, having no schematic. 

Any of those supplies should work fine.  Sounds like the Radial box takes that power and turns it into whatever it needs anyway.
Yes, the phantom power box goes between the DI and the mixer.  And it should do a better job than a passive type would do.

Hmmm

Seems like some more stuff to learn

https://www.ssguitar.com/index.php?topic=4594.30

Specifically (per G1)

"I'm not sure your test set-up, but it's critical that you do not ground the speaker (-) with any test gear, grounded load, etc."

(I was clipping my scope ground to the negative speaker terminal). 

Forum Members....

I have a Radial Pro48 Active Direct Box (non-powered) and would like to take the XLR output into a mixer.  The mixer is an older model and does NOT have phantom power.  So I am assuming I now need a 48v Phantom Power Supply.  Otherwise, will the Radial work without a DC power source?

It looks like the XLR output of the Direct box would go to the Phantom Power Supply input, and from there the output of that box would go to the mixer?  The other option is to get a passive direct box? I am a tad concerned with a loss of signal and overall sound clarity from my guitar.

I have spotted a handful of Phantom Power Supplies on Amazon, all under $30.  Some of these power supplies are fed from a 9Vac source, others use an 18Vac source. Anything in particular I should be looking for?

Thanks,  Tom

I was becoming suspicious of this guy

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albeit for no reason I just figured it looks like it gets hot and may be failing.  But then I figured it's probably not a voltage regulator since it's marked ECB and TR 201
 

Might be time for some freeze 🥶 spray since it seems like something is getting hot and shutting down.

Alright well either
-im not doing this correctly
-or this amp is putting out one watt 

So I -connected an 8 ohm speaker
-Scope leads across speaker terminals
-Maxed out aux and master volume
-increased signal until output started clipping (about 2.8 Vp-p)

Did math
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So I guess I have a sick one here 

Meanwhile it cut off a few times I could hear a distinct click whenever it did.  It was not intermittent it wouldn't come back until I turned it off and turned it back on after s moment.
And the fuse is good.
I guess that explains why all the cover bolts were missing

A couple things I noticed about this amp is there is no relay click maybe it's not supposed to have one because it "works" with out it.
Also I noticed the bottom panel gets warm
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 but I saw a video pointing out that the output transistors are attached to the bottom panel
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So right off the bat I suspect a bad voltage regulator 

I'm gonna propose that the above is probably not SOP for amp testing   

I'm gonna connect a speaker and see if I can get ear bleeding 1 khz   

Time to play with this one

Had to borrow a fuse holder cap and a fuse and put it on the big ugly DBT with 60w bulb

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Next input signal 1Vp-p and hooked scope probes to input and (16 ohm) output
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Input channel one and output channel two

Amplifier power off (ch 1 at the bottom)

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Next amplifier power on and had aux volume at half and master volume at half
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Not much amplification going on 
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Next I tried to max out both volumes and see the result but it started flattening out the top of the output

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The most output I could get is about four Vp-p

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Now...granted there are a bunch of switches on the back so who knows
And...idk what I'm doing 
So there's that but it looks like it works to me idk 

One really wierd thing that happened...I could hear a very faint hum with the power off.  I leaned in to listen better and thought wow is that my 1 khz signal ?! So I reached up and changed the frequency and yes it was my signal I could hear it with the amp power off 

Yes sir thanks
It did occur to me later that probably was kinda silly to just connect a cassette deck to it 

I need to learn about all this stuff 

Also later I noticed the "power light" flickering on then realized that is actually a "clip indicator"



Also I probably need to set this amp to the side and not jack with it since I really like it and then go to work on the single channel version I picked up.

I'll probably build the next one into the jerry can.