If you are very very lucky it might be so simple its just a bad connection in the tube socket.
Pull the tubes out and reinstall them a few times just to make sure, if you have some Deoxit give the sockets a spray.

Just remember that there is high voltages in tube amps and the capacitors can stay charged for a long long time, be very careful so you don't damage the amp when you get knocked across the room from a charged capacitor.

The only reference I have seen for that Zener is that it is a medium power zener diode, whatever that means.
http://www.wylie.org.uk/technology/semics/GEC/GEC.htm

If you have a 1 watt 13V zener then try it, check how hot it gets.
If you have to buy one then why not get a 5 watt 13v zener diode, it will look chunkier and that it belongs in the amp.
You can get 5 watt 13 v zeners for under $1 if you shop around so that is what I would do.(Mouser)

I don't think my copy of the schematic is any better on the power amp stage.
Can you take a picture of the PCB so we can see the board and components ?

Disconnect speakers before any testing
The first thing to check with power off is the bridge rectifier with a multimeter set to diode checking.
If the bridge seems ok then check the power transistors for shorts from collector to emitters. (Q110-Q113)
Check the power resistors as well (0R5 5watt).(R123 - R126)
Power on and check if there is any voltage on the + or - 63v rails to ground (0V).
Check for DC voltage on the speaker output
Do this quickly so you don't have the power on too long,turn power off and check if any of the power transistors or power resistors got warm or hot.

Hopefully one of the more experienced guys will give you more/better advice.
Cheers
Mick

The collector on T12 should not be +30.8v, it is connected to the negative rail.
Are you keeping the common (Black) lead of your meter on 0V (ground) all the time ?
It is very important to clearly indicate the positive and negative readings so the experts (not me) can work out what is wrong.
Maybe worth re-measuring the voltages ?

https://line6.com/support/manuals/podhd500x

Most pedals will not turn on unless you have the input jack plugged in, and it has to be a mono plug as well.
The input jack is acting like the power switch as well to preserve the battery when you are not using the pedal.

I am not surprised that the wall wart did not power the pedals, the polarity is wrong on the plug.
The center pin should be minus and the ring should be plus at 9vDC, your power supply is the opposite.
I hope you have not damaged the pedals with the wrong power supply.

Ok thanks I put 0.5A and 2A normal fuses in and it's making good sounds but won't make any sound without standby on

I think you are reading the switch wrong, up the amp is on and down the amp is in standby.

Slow blow fuses can also be marked with a "T" it stands for Trög which means slow in some languages. ie. T2A

That polarity switch has me wondering if that amp might be unsafe, if it switches the incoming supply wires around and there is no earth wire on the lead you might have to fix that.
It don't seem old enough for that though
Read up on death caps to check it out.

Tjenare, welcome to the SSGuitar forum as well, I was born in Sweden but moved to Australia in 1973 so I have no idea where you go for components in Sweden.
I buy most of my components from online stores like Tayda, Element 14, Mouser, Digikey etc.
You can most likely use most of them too.
https://www.taydaelectronics.com/
https://au.element14.com/?langId=46&setLangId=true
https://www.mouser.se/
https://www.digikey.se/

There are many more I use and some local ones in Australia as well.
I changed the URL's to the Swedish sites for you.
Cheers
Michael

All parts should be available except the CA3080 IC and the CA3094 IC, most people either find some old ones in some shop or they substitute them with a LM13700 IC.
One example of how to substitute the LM13700 can be seen at Aion FX L5 pedal build, look in the Build Documents.
https://aionfx.com/project/l5-preamp/

All the capacitors should be measured before buying new ones to make sure they fit, new modern capacitors are usually smaller so with the Lab series there should be no problem at all. The Lab series of amps had all axial electrolytic capacitors from memory with leads on each end of the capacitor, if you want to get new capacitors with a similar size as original then go for a higher voltage capacitor. It will cost more though.

You bought the amp in Sweden but you did not mention the country you are in now, if you mention where you are now there might be someone here who knows the best place for you to get components in your country.
There might even be someone here who lives near you who would be able to help you, you never know.

Here is how a light bulb limiter works:https://www.ssguitar.com/index.php?topic=2093.0
It is just a light bulb connected halfway along the active wire on the way to he amp, the neutral goes straight to the amp.
If you have a fault the light bulb lights up bright but you don't destroy anything in the amplifier.

Here is a copy of the schematic in case you can't read yours too well.

You can buy leads that have fuses in them, but they are not really cheap if it is for home use.
If you get the Fluke ones you still have to buy expensive fuses.
My set has a ceramic 3AG fuse in them and they are ok to use, they are a bit bulky though.
https://au.rs-online.com/web/p/multimeter-leads/0204583

If they are fully encapsulated in plastic then you just need some thermal grease.
A thin layer of grease and try to move the transistor around  a bit against the heatsink to spread the grease evenly, clamp it and solder in.
Just poke the legs through the PCB enough to solder them in, it keeps the transistors more towards the center of the heatsink.

If you mean the insulator between the transistor and heatsink then I would say yes.

I 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 and only amp plug when amps is selected, but it was many years ago.
I wonder if you can still get some like that anymore, maybe it was just a temporary fad that went for a while.

megatrav: I would really love to build my own hybrid amp with a tube preamp and solid state power amp for gigging.

Have you considered building / getting a valve stompbox from Sushi Box ?
He has valve pre-amps in stompboxes, add a DI and you could go straight to FOH.
Get a class D pedal amp and a speaker cab and you are ready to rock.
https://www.sushiboxfx.com/
https://c2celectronics.com/