BIAS procedure Hiwatt DR405

[cfortner]

Hi,

I'm building a Hiwatt DR405-clone on basis of the original circuits of Hiwatt/Huss.

BIAS is performed as a single pot per each side, the BIAS input voltage is -130 V.

But where is the testpoint and which voltage is right at this testpoint?

I assume -49 V at pin 5 of the KT88. Is this correct?

Thanks

Christian
from Hamburg, Germany

[martin manning]

I would not rely on the grid voltage to set the bias, better to target a percentage of the max anode dissipation. Ground the cathodes of the power tubes using 1 ohm 1W 1% resistors, and measure voltage at the cathodes (mV), which is numerically equivalent to mA. With 650V on the anodes, I would set something like 60% of max anode dissipation, or 0.6*35W/650V = 0.032 mA.