Hi guys,
First of all, I hope you don't mind that this post is in English. My German is not good enough unfortunately. (What we Belgians call "Jean-Marie Pfaff- Deutsch)
So I repaired an old Dual 1224 for my dad and I decided I wanted a Dual idler drive for myself. I pickuped a lot of three players with two HS39 bases for repair for €25 euros.
One of the HS39's is broken with a short circuit, but the other one works! I've had to replace the 'Knallfrosch' but other than that it works at both channels.
But now my problem:
There is a constant hum at the speakers/headphones that gets louder with the volume. Some hum is to be expected with these old amps, but I've never heard as much as with this one.
More importantly: I could hear a change in the hum when I touched the faceplate or the volume dial of the amplifier. To me that sounds like a grounding problem so I measured the voltage from the chassis to the earth ground in my house and I got 85 VAC!
I know some old amps are designed with a 'live' chassis, but 85VAC seems to be high and potentially dangerous. Especially since the dials and buttons on the front are connected to the chassis ground.
Does anyone know what could be causing this issue?
So far I've replaced the elcos in the power amplifier, but not yet anywhere else. all ground connections work as shown on the schematics.
Any help is appreciated and thanks in advance.
PS: You can answer in German, I read it a bit