• 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.

Mikael Abdellah's KT88, Loadlines

soundbadger

Member
2007-09-24 3:22 pm
can anyone help me,
i am trying to work out this scehmatic:
diyAudio

ive heard people in this forum saying that the kt88s are operating at 75mA but when i draw the load line for a HT voltage of 400v and a primary impedance of 5Kohms (like on the schematics) the anode voltage at 75mA would only be about 60v,
can anyone help me
cheers
 

soundbadger

Member
2007-09-24 3:22 pm
so should the operating point be in the middle of this ac loadline, because if 75mA is the operating current then it is not anywhere near the center of the line.

also could you explain what you mean by DC and AC conditions, how should i go about calculating my operating point and current when i know my opt primary impedance and my HT voltage.

i thought i understood this, but working through this amp i dont seem to get the same figures as everyone else

thanks

ed
 

soundbadger

Member
2007-09-24 3:22 pm
after a bit more reading of morgan jones book i think i have it.

if i do ht over rl 400/5000 i get 80mA

so if i wanted a cathode bias voltage of 37.5v i would do 37.5/0.080 and get about 470 ohm

or about 440ohm for a bias voltage of 35v


could anyone how has built this amp let me know if this sound right

cheers

ed