Grid input for parallel 814s

[kb3ouk]

I'm back to work on the homebrew rig after not working on it very much over the summer. The only things I have left to do are finish the power supply, wire everything up, and figure out how I'm gonna drive the grids on these things. My exciter is a James Millen 90800 using a single 807, with the power supply I have built for it it does one of two power levels: 5-6 watts with 300-ish volts on the plate, or 20-25 watts with 600-ish volts on the plates. From testing, it runs a lot more stable at 300 volts than it does at 600, and the data sheet for the 814s say they need approx. 2 watts of drive, per tube, so about 4 watts for the pair I'm running. What would be the best/simplest/stablest way to drive the grids on these? It's 80 meters only, and for bias I will be using a combination of fixed and grid leak to get the -150 volts the 814s need, 45 volts which is coming from the power supply for the exciter and the other 105 will come from grid resistor, which if my math is right should be around 5200 to 5300 ohms. if I have to, I could switch the power supply on the exciter to run higher power if the 5 watts isn't enough, but then that would probably be way too much unless there is some attenuation or I put some resistance in series in the supply to drop the voltage (transformer can only do either 240 or 480 on the secondary, and I'm using a full wave bridge with cap input, so that's where the 300 volts is coming from on the 240 tap, there's no room left anywhere in the chassis for a choke, or I would've used a choke input full wave bridge on the 480 tap which would've gave me around 400 volts and a little bit better power output).

[w4bfs]

hi Shelby .... input ckt can be link coupled, pi or T .... you may need to neutralize or not, layout depending .... use of a swamping resistor may eliminate the neutz need .... say maybe 10k or so ... experiment !

[kb3ouk]

I'm leaning toward the pi input, I'm assuming just design it so the input impedance is 50 ohms and the output of it is around what the grid input of the 814s would be, a formula I found in an old ARRL handbook worked out to be around 10000 ohms for the grid input for those tube. Could I get away with fixed component values for the input?

[K7LYF]

The Hallicrafters HT9 uses.  A single 814. You might look there for ideas.