• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Driver stage for SE KT88

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You need to also include a 1K grid stopper for the 10M45S. And a 2K2 or thereabouts carbon comp on the grid of the EC86. A 47-100R carbon comp between the anode and the CCS can be used to hedge against Oscillation in the UHF region.





And sometimes it is required to RC filter de B+ supply to get the voltage above the CCS at about 300VDC. You then drop about 150V across the 10M45S. This R is about 100 Ohms per volt of drop. So say your coming down from 400 you need a 10K resistor for the RC filter section with a 3W wattage rating because the resistor sees about 1W of dissipation.




Current set resistor is 330R for about 10mA +-1mA you can also use a parallel combination of 680R and a 1K pot. This way nothing breaks if the pot goes open circuit for some reason.


At 150V and 10mA working point your looking at about -1.8V grid bias, measured with the MK1 eyeball. A run of the mill red LED will give you a drop of about 1.8V at that current.


I have used the IRF820 quite a bit in the past as a source follower after a 12AX7 to drive a typical Marshall/Fender tonestack. Does very well!


What do you think about using an IRF820 in the same fashion here? (after an EC86 150 plate volts run about 10ma with CCS)? I could run the IRF820 approx 10ma with a 15k resistor to ground.



And I think I will connect the KT88 UL, not triode.
 
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