Hi everyone, this is my first post here.
I apologize for writing in English, on this mostly German forum, but my written German is something I like to spare you.
I can read it well enough (French as well if needed).

I finished the AC18 last week, and it wa working perfectly. But, when unmounting all pots and connectors, in order to attach the face- and backplates, I apparently create a short across in 2 and 3 of V4 (one of the EL84's).
Now the amp has a hum and the volume knob behaves strangely.
When the volume is at max, the amp actually sounds normal (just very loud, as it should). When the volume is at 25% the volume is still rather loud, but it sounds like a gated fuzz.
With the volume down completely, the sound is still rather loud, but fizier.

If I measure R14 & R17, R15 & R16 and  the values across the dual pot the values are still symmetrical across these parts in the two paths from the power tubes to the dual pot.

Any idea where to start looking from here?


BTW
Total beginner question, when I start measuring the voltages as written in the schematic, do I measure thes with or with tubes in place?

SOLEVD.

I found the culprit!!!!

Apparently I fried the powertube.
Just replaced the EL84's with some spare ones I had lying around, and the amp works beautifully again.