Hi all,

I apologize that I'm writing in English, but unfortunately, my German knowledge is not existing )
I have bought and built the Marshall 18 watt kit from this site and it works, but only when I'm below 6 on Volume. If I crank it up higher, I get this oscillation (?) problem.

Video of the problem: https://www.youtube.com/watch?v=FirjbD_hppI

I tried to poke around with a wooden stick and touch things in the amp, but I could not find the issue.
Has anyone faced this issue yet, or do you have an idea, where should I look?

Thanks, folks!

Hi, may be the link in this thread is helpful:
http://www.tube-town.de/ttforum/index.php/topic,15106.msg149054.html#msg149054

If not than please post schematic with your measured voltages and a clear pic of your built.
Cheers
Gerhard

since there is no feedback,reversing output transformer wires does nothing.
most  probably its a parasitic oscillation,it can be a wire too long or in the wrong position,a bad or missing ground point,a bad soldering.
Try separate the grid wires from the rest.
Check for continuity on all supposed ground points.

you connected something wrong, take some photos of your setup and put them in here
does something change if you turn on the middle regulator?