Since the tube of the month series comes to an end soon, I picked a special tube for this months presentation. I'd like to show the biggest tube type in my collection. Meet the almighty 851.
The 851 is one of the largest air cooled transmitting triodes with its gargantuan bulb diameter of about 15cm and overall height of more than 40cm.211 as the perfect driver tube for the 851. Connection to the tube happens from both sides through a large plate cap at one end and two thick filament pins on the other. The grid is connected through a blade which is located between the filament pins. The connection is the same as with the 849 the little sister of the 851. For a complete set of technical parameters see the General Electric data sheet. Obviously creating an amplifier with this tube would be a daunting task. When I first saw a 851, I had to have some and I contemplated building an amp for it. Initial planning resulted in at least 3 chassis per channel, one for the high voltage supply, a filament supply chassis and the actual amp. Still each chassis would be quite big and heavy. Who knows maybe one day I will work on such a beast.
The plate curves from the data sheet above and the plate curves taken with the curve tracer. Due to limited voltage range of the tracer only up to 400V and with grid voltage steps of 2V:
And now some series toob porn:
Here we have a General Electric 851 in all its glory.
What a massive slab of graphite as plate!
Close up of the filament tension springs:
Two of my 851s:
I also have two sets of suitable sockets: