Ef86 preamp stage plate voltage too low

[cservonyec]

I am relatively new to this forum but I can see some really experienced guys here. So here is my little problem. I've just been trying out a new preamp stage based on the EF86 valve. I've used 100k for the anode (plate) resistor, 470k for the screen grid resistor and 2.2k bypassed with a 25mF cap and a 100nF cap from the screen grid to earth. The amp is working and the gain is very high. The B+ is about 270V. There is hardly any voltage drop on the screen grid, but the plate voltage is about 36V. My instinct tells me that the plate voltage should be higher than the screen grid voltage, but when I measure them this is what I get. Could it be caused by leaky cap, or cap that became open? Any ideas?

[loudthud]

You need to go up on the screen resistor or the cathode resistor.

[cservonyec]

I am relatively new to this forum but I can see some really experienced guys here. So here is my little problem. I've just been trying out a new preamp stage based on the EF86 valve. I've used 100k for the anode (plate) resistor, 470k for the screen grid resistor and 2.2k bypassed with a 25mF cap and a 100nF cap from the screen grid to earth. The amp is working and the gain is very high. The B+ is about 270V. There is hardly any voltage drop on the screen grid, but the plate voltage is about 36V. My instinct tells me that the plate voltage should be higher than the screen grid voltage, but when I measure them this is what I get. Could it be caused by leaky cap, or cap that became open? Any ideas?

Thanks a lot for the advice. I will try that at the weekend. My idea is actually not my idea, but what I was trying to do is to rebuild a Dallas Rangemaster amp, that I had long ago. Unfortunately I don't have the amp anymore, only a handful of pictures from the inside. From memory it never had that insane gain from the preamp, and it had that strange feedback solution by a 1 or 1.2Mohm resistor connecting the input grid to the top wiper of the volume control where the decoupling cap connects for the next stage, which is half of an ECC83. After that there is a strange tone stack followed by a cathodyne phase inverter style push pull pair of 6BW6.
Here are some pictures. The big resistor is actually a 91kohm. Just behind the volume control's top leg (the top of the picture is the bottom leg of the volume pot where the earth is connected.) there is a horizontal wire and it looks as though the decoupling cap is connected to it but that is just an illusion from the picture. That is just the earth rail in the background and the blue electrolyte cathode bypass cap is connected there.
My next task will be to figure out the tremolo section and I may need some help there folks.
Thanks again.
Laszlo

[cservonyec]

You need to go up on the screen resistor or the cathode resistor.

Thanks for the advice I've raised the cathode resistor to 3.3k and the screen grid resistor to 680k. Now it is more in line. The grid voltage now is a lot less then the plate voltage, perhaps I should have left it a 470k. Ah well, more tweaking ahead.
Cheers.