• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Telefunken EL34 data sheet

dgta

Member
2011-05-30 8:08 pm
Looking at the Telefunken data sheet for EL34, op points for PP AB. There is Va, there is Vg3=0, but no Vg2. Instead, they give an Rg2 value with a note that it is common to the 2 tubes. Does that mean Rg2 is connected to the plate supply (i.e. OPT center tap)?
I've seen Vg2 specified to be the same value as Va, but not in this manner. Is there any special meaning or reason to do this?
 
dgta said:
Does that mean Rg2 is connected to the plate supply (i.e. OPT center tap)?
Yes, probably. Specifying a resistor is not quite the same as specifying a screen voltage, as the resistor is partly self-adjusting. If a particular valve draws more screen current than usual then the screen voltage drops a bit to reduce the current. With a pair sharing a resistor you need to hope they are reasonably well balanced. Alternatively, give them one resistor each (of twice the value), but then it will need good decoupling.