This is the schematic for a Champion 40.  Not sure which PR, but it has DSP and the output IC is TDA7294.
PR number is 'production release' and does not necessarily mean it uses a different schematic.  Schematics go by model name and revision number.
Check if this schematic matches your unit.  If not, what is the output IC in yours?

When the fuse voltage rating is less than the circuit requires, the possible arcing is more likely after the fuse has blown.
Your probes have a voltage safety rating as well, and that would be lost with any modification of the probes, no matter how high the fuse rating.

Lots of modern electronic equipment has standby circuitry that is always running unless you unplug it from the wall.

The metal tab type has not been made for over 10 years, if you found some they are old stock or possibly fake.
Like Jazz said, you don't need the spacers for the plastic backed type.
Attached datasheet shows both types.
*EDIT TO-247 package does not have the back insulated and requires insulator.


If you do happen to have found some old style metal tab types, you not only need the mica spacers, but also special plastic washers for the screws.

Quote from: Tassieviking on February 26, 2024, 10:31:55 AMI have seen multimeters that physically block the holes when you turn the knob so it is only possible to use the volt probe when volt is selected

I think if you forget you were in current mode, you will likely to forget to turn the knob as well.  So then you would still do damage with the probes, which are acting as a straight piece of wire in current ranges.
My current range require switching ports, and there is a beeper that goes off if I choose any other range while plugged into the 10A port.
Still doesn't help me if I forget to switch range.   

$30 is for a 2-pack, looks like you can't buy them separately.

Plug your guitar into the 'power amp in' jack, is the hum still there?

Quote from: Tassieviking on February 22, 2024, 12:01:47 PMIt is usually a M205 fuse that costs cents, sometimes a ceramic type but still cheap.

My meter uses a regular fuse for the 2A range but has a special fuse for the 10A range (that has it's own probe port).
The special fuse is very expensive due to safety ratings and odd size.
You can find cheap ones from China but I think they are fake as far as the safety ratings go.
Mine is not a Fluke, but this will give you an idea:
https://www.fluke-direct.ca/online/fluke-instruments-replacement-fuses

If the hiss is so loud that the amp in unusable, it is likely a noisy transistor is the cause.
If you understand the signal path, you can try a cap to ground at various points along the path to try to isolate the location.  Something like 0.1 or 0.47uF rated 100V or more should work.
If the cap to ground kills the hiss, you know the source is somewhere ahead of that in the signal path, so you move the cap further toward the input and try again.

I think if you tweak it to get symmetrical you will still overdrive the stage anyway.  And it won't sound any better if it's clipping evenly on both sides rather than just one.  It's not really meant for that kind of guitar signal.
Some tubes amp do that as well, the gain stage before the volume control clips unless you turn down the guitar volume.  Just that with tubes no one really minds as much because the clipping is softer.

You can tweak the gain of the stage to deal with it, but you might just find the next stage or somewhere down the line clips the same way.

That's why I suggested getting full unclipped output and seeing what kind of input signal level that requires.

Have you verified that the input stage is the first thing that clips before the amp gets to full power?  Seems odd that they would have such little headroom at that stage.
At full power (just before clipping) into a load, what is the peak to peak voltage coming out of the first IC ?

Where did that example come from?  Why did they say the biasing resistors should equal R1?
The ratios are about RF and Rin and set the gain of the non-inverting op amp.  Your circuit and the example circuits have different gain so the "=1/2 R1" does not apply.

See this page:  https://sound-au.com/articles/gyrator-filters.htm

When you are getting the 1V from E-C, short the base to the emitter and see if the reading goes to open circuit.  If so, it should be ok.

Yes, it is possible for electrolytics to self-heal.  Whether it is temporary or permanent is another question.