You need a bias meter. The amps draw a fixed bias of -52 for a 60/100 and -52 Volts on the 6L6's with -46 on the outer sockets for Simul-Class amps. Export model bias is different as well, but no manifesto today.
The tubes you have all have a natural plate current which is the amount of negative voltage they will draw. The higher the natural plate current the more negative your bias will be. So, basically, the hotter the tube the more negative voltage it will draw and will bias in what some would define as hotter. a tube that draws less natural plate current will draw less negative voltage and may be defined as colder. Finding out if where your tubes relate is why you need a meter. not only will it show you the current draw / bias at your fixed values, but it will tell you how well your duet or quad is matched. 5ma is considered a good match to prevent an imbalance in tone or hum from tubes that are 20+ma mismatched.
Anywho, once you know what negative voltage you are drawing on a tube, you need to know if the tube can handle the amount of bias it is set at.
For instance:
6L6 = 30 Watt tube
EL34= 25 Watt tube
7581A - 35 Watt tube
When you are ready to read the bias of a tube you need to know the plate voltage. A IIC+ with the 105 ranges from 480-483. To get the optimal bias of any of these tube you need to know how to determine what the tube can handle at any particular plate voltage. I would tell you how, but I prefer that you live for the time being.
So, at 480 volts each tubes optimal maximum plate dissipation is usually factored at 75%. Commonly known as MPD.
Mathematically you take the following equation.
Tube Wattage - 6L6 = 30 divided by 480 ( plate voltage ) = .0625.
Multiply .0625 X .75 ( optimal % MPD) = .0468. Drop the 0 and your optimal bias for 75% MPD is 46.8. Anything at this number or lower is fine.
When you get your reading and you want to find out what % of MPD you are running, lower the % of MPD until you get near what you are reading.
Say you get a 31. you are running at 50% MPD etc.
An EL34 at the same figures would optimally run at 39ma.
I personally find Boogies too muddy at 75% and prefer them between 22-35ma. Too low is a bit grainy and harsh, but it's generally what you get when you are running at 17ma from a Mesa Yellow 6L6. Too high an your just burning the tube out for mush and asking to take some components with you.
Each tube type should then read within 5ma of each other to be considered a matched set.
Plate voltage is read at pin 3 of the power tube to ground. I would work on using a ground clamp and keeping your left hand behind your back for a while before trying 480+ volts. It can and will kill you. The negative voltage is read at pin 5 to ground on the tube socket. This is basically what the amp is feeding the tube, not necessarily what it's consuming.
A IIC+ will read, in most cases exactly what it is supposed to -52 on a 6L6 and -46 on a Simul outer socket with a 6L6 or EL34.
Another bias method to avoid for now is the shunt method. If you want to try your hand, get a bias meter like a Bias King, Allesandro, Weber or Ruby bias meter. It's makes life safe and easy. Also, a 1000V DC Meter will be needed. Don't cheap out here either. The safer the better and fuse protected.
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