Bias circuit and cap orientation

[BlueX]

I am confused (just recently, not "for so long it's not true") on cap orientation. On Robrobinette excellent site he states "If your amp has a fixed bias circuit make sure its bias filter cap(s) are connected + to ground because they deal with negative voltage.". However, both on the 5E3 and 18W I've built the "bias cap" is oriented with negative to ground, and positive to cathode (6V6-p8, and EL84-p3), according to each layout. On other schematics, like British 45 or Blackface kits, it looks like the cap is oriented with positive to ground.

Have I mixed things up here? Is "fixed bias" something else than what's in 5E3 or 18W? Grateful for any clarification!

 

[StingRay85]

Fixed bias means that you have a fixed negative bias voltage on the grid. Therefore indeed the + side of the capacitor (smoothing the bias voltage) should be grounded. The cathode is grounded in a fixed bias amp.

5E3 is cathode biased, which is basically a resistor + bypass cap, just like for example an ECC83 is typically biased.

 

[BlueX]

Fixed bias means that you have a fixed negative bias voltage on the grid. Therefore indeed the + side should be grounded on the cap. The cathode is grounded.

5E3 is cathode biased, which is basically a resistor + bypass cap, just like for example an ECC83 is typically biased.

Clear answer, thanks!