Sorry I don't have anything more for you to try.  These are the worst kind of repairs, qualitative judgements that are just borderline 'maybe' worse than normal.
I have been in your shoes before and spent way too much time only to find there is no fix within economical means.  Sometimes it turns out the owner's memory is 'rose-colored', or they have changed something else in their rig that they are overlooking.  Or they have something in their environment that makes it worse at their location and what you are hearing is not even what they are complaining about.

That's awesome, thank you. I've considered building a class A for audio, didn't know it could work for guitar as well.

So, is it safe to say that the main difference between guitar and audio amps is in the "preamp" section?

Tube pedals can be a lot more dangerous, all the C2CE pedals have high voltage inside them even though they run on 9v-12v. I think all the C2CE pedals have between 240v to 300v inside them. The owner of C2CE also runs Sushi Box FX which makes pre made pedals that all have tubes and they can run up to 360volts on the internal tubes just like a real tube amp.

Thank you for your reply.

This amp belongs to someone else who insists the hum came into it recently.
To me it sounds a little noisy.I have heard quieter ones.I don't know anyone with the same model to compare.
I guess I will just have to give up on this one.
Thank you for all your help.

Those readings across the speaker are within what is considered the normal range for hum in a guitar amp.  Are you using it in a particularly quiet environment?  Do you have other amps you have compared it to?

Thanks for coming here - I'm always glad to have a new face and I love the idea of building a fully discrete practice amp.  I've had thoughts to do the same myself and haven't had a chance to do so yet.

Honestly, this isn't nearly as large a task as it seems.  For the preamp side of things, you can use any discrete pedal amp circuit that you like the sound of.  You can either keep it as-is, or find one you want to modify.  Something like Jack Orman's Mosfet Booster, RunOffGroove's Peppermill, or even my 5th Gear Overdrive would make a good gain stage.

You could make the booster for the initial input, go into a tonestack of your choosing (see Duncan TSC in the web for ideas), then go into another gain stage for recovery and drive (like the 5th gear OD).

After the preamp is complete, you could send it into an amp from Rod Eliot, like his project 10 - a 20w Class A discrete amplifier.

Whatever options you choose, definitely come back and let us know how it goes or if you need help!

If you do well with hundreds of thousands of options to sift through, this new little guy might be for you.  It sounds pretty fantastic, packing 24watts of power into a tiny little box.  Link it to your phone and you have over 200,000 NAM patches available at your fingertips to load onto your new amp.  It can store 5 of them locally that you can bump through without using your phone, which I highly recommend.

MSRP is $229 USD and these are available today.

https://www.premierguitar.com/news/blackstar-beam-mini-desk-amp

I will have to rewrite my last post as it doesn't display properly on a phone.
It was perfect on a laptop.

Q34 B-E -437MV
R321 0MV
Q36 B-E +543MV
R320 1.3MV
Speaker 21MV DC 9MV AC


Q34 B-E -592MV
R321 3MV
Q36 B-E +573MV
R320 4.5MV
Speaker 23MV DC 12MV AC


Q34 B-E -612MV
R321 11MV
Q36 B-E +588MV
R320 12.3MV
Speaker 22MV DC 20MV AC


Q34 B-E -625MV
R321 22MV
Q36 B-E +600MV
R320 23.1MV
Speaker 25MV DC 30MV AC

Thanks again.

Here are the results of my tests.

Q34 B-E    R321           Q36 B-E       R320          Speaker voltage

-437MV     0MV           +543MV        1.3MV        21MV DC    9MV AC

-592MV     3MV           +573MV        4.5MV        23MV DC    12MV AC
 
-612MV     11MV          +588MV       12.3MV        22MV DC    20MV AC

-625MV     22MV          +600MV       23.1MV        25MV DC    30MV AC

I hope this makes sense to you.   
Ps I have just discovered this does not display properly on my phone. It was ok on the laptop, so I have rewritten it. Please see my next post.

Thanks for the feedback. Which pedals are more difficult to make, with tubes or without? Or is there a significant difference at all?