Looked at the 811 specs.
Should expect 'something' at 400 on the plate.
The graph shows plate current vs grid voltage.
Alas!...my 811 grid pins have NO wires!!
Guess it's not a grounded grid amp ??
Photo attached.
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It is grounded grid. Notice the ceramic caps from grid pins to ground and the coaxial cable, you wil find, probably goes to the grid meter shunt. Notice the capacitor from the filament to somewhere? it probably goes to the amp input. There may not be a T/R relay inside the amp. I didn't see one, but the pictures do not show enough. I believe the empty pins are pin 2.
400 Volts will get you very little output. With a normal high voltage of at 750-1500 it will make output with one tube, but probably less than half of the total amount since the PI circuit tank will be made for two tubes and therefore present half the impedance to the one tube, which is an overload. Using a low-ish Hign Voltage may improve the match situation since the plate voltage swing will be lower with the same plate current, making the expected impedance of the tubes lower and therefore closer to using two tubes at a higher voltage and double current. The driving impedance of a pair of 811s is about 150 Ohms. It's not critical but a 1:2 step-up toroid may help, though you should try to use a broadly tuned L circuit for each band. These articles might help:
There is an article for one grounded grid 811s at 1500V that may help you see what's going on. It says 200 watt, but that is input, not output. Two 811s can make about 200W out, more on SSB's low duty cycle. Also refer the to tube manual and use the audio ratings for two tubes in push pull class B or AB2, which will give an idea of the acceptable operations.
http://www.qro.it/amp/schemi/pdf/68hb187.pdfThe heathkit SB-200 is a two-572 amp, but you can use 811As in it. The tubes are almost alike except the 572s have more plate dissipation. It would be a good amp to be the example for upgrading yours.
https://www.w6ze.org/Heathkit/Heathkit_033_SB200.pdfThere's a video on tuning up 811 amp, His has 4, but the ideas are the same.
https://www.youtube.com/watch?v=MTt6QtgsIFYBe careful and watch the grid current, it is easy to burn up the grids on 811s, since they are smallish tubes. A 100W radio will destroy them. A rule of thumb is that the lower the plate voltage, the higher the drive wattage. but not always.
And indeed some people push 811s to 2000V. They will take it but be careful especially with any questionable tubes.
hope these items help. Please send full pics so everything can be seen.
