FWIW, I made the following measurements tonight on my Drake TR4-CW: All made in SSB mode either with rig in Rx mode or mic keyed but mic gain at minimum to check bias voltage and idle current. Final tubes numbered from back of rig towards front of rig 1 through 3. Tx measurements made after adjusting idle current per manual while viewing front panel meter for 100 mA. Bias voltage measured from pin 2 of center tube (anywhere along flat copper strip connecting grids) to chassis ground Rx: -47 volts Tx: -46.5 volts Cathode current measured across 15 ohm cathode resistors with mic keyed (resistors checked individually with zero'd low resistance ohm meter and all new as of last month): Tube1: 398 mV ~26.5mA Tube2: 580 mV ~38.7mA Tube3: 508 mV ~33.9mA Total idle current ~99.1mA So it looks like Tube 2 (middle tube) is carrying the lion's share of the current but together the three carrying close to the desired 100mA of idle current. Screen voltage measured on each tube pin 1 to ground: Tube1 Rx: 246.6V Tube1 Tx: 236.2V Tube2 Rx: 246V Tube2 Tx: 237.8V Tube3 Rx: 246.5V Tube4 Tx: 237.9V Hope that yields some clues.