First ECL82 amp probs.

[the_rod]

Hello All,
I'm quite a tube noob and I'm making my first amp, based on this schematic:
schematic

I only modified the power supply to add an insulation transformer. After a bit of experimenting I got the amp working - well, almost. When the volume pot is at max, the amp works well and I get a great sound, and when it is at min I don't get no noise at all (how it sould be...) the problem is in between: if I move the pot from the max or min position I get a loud siren-like sound! Does anyone have any pointers on what I may have done wrong?
thanks a lot,

Rodolfo

[the_manta]

Hi !
You probably built an oszillator due to wiring capacities. When you build with combined Tubes like XCL82 and especially XCL86 you have to be careful and you must use a deliberate layout. Only use short wires ans never put to wires from different sections in parralel for longer distances. I used ECL86 for my first tube experience, but luckily it worked fine, but I know the problems you have. The best beginner tube amp still ECC83 + EL84...

Hope this helps

Simon

[Sherman]

The first thing I would try is putting a 220 ohm resistor at the grid of the triode. A 1/4 watt resistor should be fine there.

Remove the wire connected to the grid (Pin 1 in your schematic). Solder one lead of the resistor directly to the pin on the tube socket then connect the other resistor lead to the wire you cut.

Also, I would recommend using shielded wire from the input to the volume control and from the volume control to the grid (or the new resistor you just installed).