The 6W6 has been brought up many times in various threads, lots of positive comments about triode operation. Tubelab has had some comments about runaway in triode operation when running closer to the normal sweep duty ratings. (300V plate, but only 150V screen rating, so triode operation easily exceeds the stated screen rating.)
The one data sheet I could find floating around from RCA gives a triode operating point at 225V, -30V, 22mA. I'm considering for duty as a headphone output stage or perhaps a push-pull 300B driver stage, running around 190V, -23.5V, 25mA. This gives Pa of 4.67 watts, and spice models suggest screen dissipation around 320mW. Obviously this still exceeds the 150V screen rating, but I doubt everybody using 6W6's in triode are running that low. Those screen dropping/shifting circuits could help, but I'd be nervous about how low the screen voltage would get when driving 300B grids, for example.
If anyone has been running some in triode mode and gotten a good long lifetime out of them, what operating point are you actually running at? I haven't seen many definitive comments about op point. Price does seem to be creeping up, and though I have a couple nice pairs already I'd rather not abuse them unnecessarily.
The one data sheet I could find floating around from RCA gives a triode operating point at 225V, -30V, 22mA. I'm considering for duty as a headphone output stage or perhaps a push-pull 300B driver stage, running around 190V, -23.5V, 25mA. This gives Pa of 4.67 watts, and spice models suggest screen dissipation around 320mW. Obviously this still exceeds the 150V screen rating, but I doubt everybody using 6W6's in triode are running that low. Those screen dropping/shifting circuits could help, but I'd be nervous about how low the screen voltage would get when driving 300B grids, for example.
If anyone has been running some in triode mode and gotten a good long lifetime out of them, what operating point are you actually running at? I haven't seen many definitive comments about op point. Price does seem to be creeping up, and though I have a couple nice pairs already I'd rather not abuse them unnecessarily.
The datasheet suggests 225V as a "triode connected amplifier" and max 300Vdc or 1200v peak as a "vertical deflection amplifier", also triode connected. 190V should be perfectly safe.
Triode Wiring generally:
The plate draws the majority of the electrons, versus the screen which is at the same voltage.
You can add a 100 Ohm resistor from the screen to the plate.
Measure the voltage across that resistor (carefully, with a floating DMM). That voltage drop/100 Ohms = the screen current.
Multiply that screen current x the 190 screen volts = quiescent screen dissipation.
The original 807 data sheet only listed Beam Power operation. The screen maximum voltage was 300V.
Later 807 data sheets, added Triode Wired operation. For that mode, the screen maximum voltage was 400V.
The plate draws the majority of the electrons, versus the screen which is at the same voltage.
You can add a 100 Ohm resistor from the screen to the plate.
Measure the voltage across that resistor (carefully, with a floating DMM). That voltage drop/100 Ohms = the screen current.
Multiply that screen current x the 190 screen volts = quiescent screen dissipation.
The original 807 data sheet only listed Beam Power operation. The screen maximum voltage was 300V.
Later 807 data sheets, added Triode Wired operation. For that mode, the screen maximum voltage was 400V.
Last edited:
Run mine at constant current of 30 mA, with fixed bias adjustment set for 230V plate.
No issues, sounds great. Used as driver of 300B SET.
No issues, sounds great. Used as driver of 300B SET.
I did fry a few tubes during attempts to run the 6W6GT and several of the many variants at the published TV vertical sweep ratings. The GE data sheet shows a TV vertical sweep rating of 300 volts plate and screen with 60 mA of DC cathode current. This adds up to 18 watts of power being dissipated in the tube at idle. In my testing, I melted a couple tubes. How can you put 18 watts into a tube rated for 7.5 to 12 watts depending on how you "interpret" those specs? My tubes overheated which led to them becoming gassy and eventually running away.
What I did not realize at the time is that the sweep sections of a TV set NEVER idles. It runs at full output forever. So, if you put 18 watts of DC into the tube and draw about 10 watts of "audio power" out of it the tube is only dissipating 8 watts, where it will live long and prosper. The horizontal sweep (line output) section of a TV is essentially a current source that is switched on and off, but the vertical sweep (frame output) is a class A linear amp that is optimized to work with 60 or 50 Hz sawtooth waves. As I, and several others like Bottlehead found, the entire vertical sweep section can be lifted from a TV set, including the OPT, and repurposed as a good quality audio amp, after breaking the feedback path and inserting an input jack.
The screen grid doesn't care, or even know about voltage. It knows about total dissipation averaged over time. When the plate voltage dips below the screen voltage on audio, or other peaks, the electrons normally headed for the plate will go to the screen grid causing a momentary overload. As long as this, averaged over time, stays below the dissipation capability of the grid wires things will be good. Hot grid wires can outgas impurities and metal ions that pollute the vacuum in the tube leading to all sorts of unwanted current flow and eventual runaway. A glowing hot grid wire can actually emit electrons which will travel toward the plate often causing the tube to turn into a flash bang grenade. This will not happen in a triode wired tube since the plate and screen are at the same potential. I did have some rather surprising events in my early attempts at screen driven sweep tubes.
You should have no problem at 200 volts. The 50L6 tube seen in thousands of old radios survive forever with about 140 volts on both screen and plate. The 50L6 is a 50 volt 6W6.
Look for some 6DG6GT's. They ARE 6W6GT's. See the text in the upper right corner of the Sylvania data sheet. I got a box full for $1 each a few years ago. If odd heater voltages are OK, the 25L6 is also a 25W6 and some tubes actually carry both numbers. The 12L6 is a 12 volt 6W6, but the 35L6 is NOT the same.