jackthehack said:
"Biasing" involves setting/adjusting the plate dissipation of the power amp tubes are in line with what your tubes are rated/amp circuit design, here's a primer:
http://www.diyguitaramp.com/bias.html
I read that page, and it is complete, total and incontrovertible BS. Its not worth the read. It will corrupt your way of thinking about bias. Its factually errant, except save maybe.. maybe if you're running class A, grid bias.
The more I see, play with and experiment with tubes, the more I see many of the "old ways" are best.
There are two schools of thought -
1. Bias using a scope, looking at the crossover notch - observed at the output transformer secondary (the speaker)
2. Bias by setting the idle current of the tube to a certain point.
Both are not optimal. The first because the notch is hard to identify optically on the screen of the scope, the second because setting the idle may or may not be great for when you're running cranked up.
By far, the better way is to observe the current flow of each tube, on a scope, by means of the IR drop on a resistor in series with the tube (on the cathode).
BTW, the use of a 1 ohm resistor is fine. Think in terms of 200ma (max) being run through it. That would be 1/5 of a watt. Double it for safety, that would be 2/5 of a watt. Sounds like those 1/2 watt resistors would be fine (the doofus on that page is an idiot with ohms law).
While observing the output current, under load, into a load, you can then see just how much current is being used under load, determine total dissipation, and exceed it by the margin of your choice. Yes - exceed it - by what sounds good, and that point, dear ones, is HIGHLY variable, dependent on even the guitar being plugged into the amp. So, take another Gerald Weber "GOSPEL" fact, and toss it.
(end soapbox.. yet again)
