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In the Forum: Melquiades Amplifier
In the Thread: Bias help
Post Subject: 25-30mA or 15-17mAPosted by G on: 4/13/2018
I double checked and everything seems connected ok. all parts values are correct. I have measured the voltage across R2 and it was 208V so 208v / 15k = 13.86mA. I connected 1r resistor between M and R2 and it was 14mA. also connected 1r resistor between cathode and ground and got the same 14mA.
next I changed the R5 with 20k trimmer. shorted input adjusted trimmer to get -3.5v and the current increased to 16-17mA but the plate voltage dropped to 160v. if I increase the bias to -4.4, plate goes back up to ~195v current drops to 14mA.
Also tried swapping 5 tubes but the difference was +-1mA
25-30mA seems like imposible. something is still not correct.
In some of your old posts you said that the current should be 15-17mA so I am a bit confused now as to which one is correct:-
“10) Now you need to adjust the amount if bias on the tube in order to have 200V on plate. You understand that amount of bios is irrelevant and it would depend from the given tube of yours. Averagely the minus 3.4V-3.5V will give you 200V and 15-17mA of plate current. Do not be too finicky about it – the current in the driver tube in THIS application is not really critical. Set plate voltage between 170V and 200V with whatever bias voltage it will be (let presume -3.4V+/.5V)”
“I usually get around a year out of 5E6P driving it at 17mA and 200V. I do not know how much I will get out of 5E6P at 35mA as I use them in the single-stage amps.“
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