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BIASING 12000 Series
Posted: Sun May 22, 2011 8:15 am
by born_hard
Hi,
i would like to BIAS the 12000 Series Metropoulos 68 Plexi amp. Plate Voltage is 450 Volts. How much would you Bias Idle Current???
Isnt the Plate voltage 450 Volts very low??? I´ve heard it should be about 500 Volts?
Thanks
Aron
Re: BIASING 12000 Series
Posted: Sun May 22, 2011 10:13 am
by Roe
bias where it sounds best without redplating, usually between 50% and 75% diss
Re: BIASING 12000 Series
Posted: Fri Jun 03, 2011 2:50 pm
by wrea398
If you used the Metro trannys you should get around 495v at the plates. I have about the same 450v voltage in mine but I am using a 460 B+ volts tranny from Mercury MAgnetics. I get around 450v after warmup. I bias it at 35.5 to 36 volts. The math works out to a maximum of 37-38 millivolts on Pin 8 but I play it safe at 35-36. Still sounds great! The math equation for 70% dissapation is: 17.5 divided by the maximum plate voltage. (example: 17.5 divided by 450v = .0388 or approximately 38mV). You have to measure the exact voltage at PIN 3 on all 4 of the EL34 sockets. The highest reading is the number you use for the math. This is a good "BASE" for what you need to do. Roe is right. Go for the best sound to your ears without seeing the tubes start to redplate (glowing plates). BTW... What transformer are you using?
born_hard wrote:Hi,
i would like to BIAS the 12000 Series Metropoulos 68 Plexi amp. Plate Voltage is 450 Volts. How much would you Bias Idle Current???
Isnt the Plate voltage 450 Volts very low??? I´ve heard it should be about 500 Volts?
Thanks
Aron