Hi!

What value do you think is the grid voltage polarity of the GM70 and GM70's katod from??

Your schematic will not work.

First, the bias supply and bias regulation are wrong.

In your schematic the dual supply has a reference to ground anyway..... can you see it?

**If we suppose ** that you have a correct dual supply for U5 and the negative voltage is -270V then your bias for U5 will be very close to -270V because between -270V and the grid of U5 there is

**only** R10. Can you tell how do you calculate -50V?

The current in R10 can

**only** be its grid current which is very small (tens of microampere in worst case). The only case where you have a substantial current draw is when the grid voltage is positive respect to the cathode!

In your schematic the cathode of U5 can only be positive because its plate is at positive voltage and the choke is connected to ground.

Then apply the ohm's law: choke resistance x U5 current = (positive) cathode voltage. This is the answer to your question in the schematic.

Why do you think it is negative?

What happens if you remove the ground from R9-choke node and put the 0V terminal of the dual supply to ground?

In your original schematic you can bias the GM70 increasing a lot the value of R3 (few hundreds ohm) but this will be a self-bias! However if R3 is 4.7 ohm like in your original schematic the bias will be close to zero volts. However the driver is not working yet...

Please answer the questions otherwise I cannot help you.

I am afraid I cannot draw a schematic because I don't have any software.....

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