initial settings

[jono]

Hi Quick question do i need the tubes in when i do the feedback and bias cheers

[EWBrown]

You can pre-set the potentiometers without the tubes inserted, and with the power turned off, and the unit not plugged in. Make sure that the caps are fully discharged before proceeding.

The four cathode resistor settings should be 400 ohms each (measure from the EL94 sockets, pin 3, to ground) , initially, and the feedback pots set to 27K for 16 ohms, or 19.2 K for 8 ohms. This can be measured from the NFB location on the screw terminal strip,
disconnected from the transformer secondary.

Once the tubes are inserted and the amp powered up, and allowed to warm up for a few minutes, then check the cathode current readings (across the 10 ohm resistor test points) the current should be set at 35 mA per tube, or 0.35V at the test points.

If you measure to ground, then add 1.3K to the total, i.e 28.3K or 20.5K from each NFB to ground.

These settings should be good as-is, but you can always experiment later, increasing or decreasing the NFB will alter the sound somewhat, it is a matter of personal preference.



HTH

/ed B