Turns out his problem was a power source chain in his pedal board 
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So the amp cutting out is fixed? If so, that's good news!
Originally the amp started to crackle and lose volume on the high gain channel when it was cranked. ... So when this issue happened, I looked at my tubes and noticed in the middle of the 12ax7s I had an old groove tube (that was pulled out of my Kistom 72 coupe from about 3 years ago) so I right away said "well theres the culprit.
I have preamp tubes that have sat in the same amps for 10-15 years, with occasional use, that still function fine. Most of the preamp tubes I have are not new production, but were pulled from old equipment. They last a surprisingly long time compared to what you're led to believe by tube sellers.
Now if you told me the tube felt loose & wiggly in the socket, it could be the tube was not making good, solid contact with the socket pins. That could cause intermittent cutting out.
Notice also the way the High gain channel uses the switched contact on the Low input jack to switch in an extra gain stage when you unplug from the Low input and plug into the High input. That switched contact could be dirty and result in cutting out only on the high gain channel. Logically, if the 2 channels share 95% of the same circuitry, and the problem only happens on the High gain channel, then the problem lies in the circuitry that's unique to the high gain channel.
... on the topic of bias. I wanted to ask a question to better understand. I know bias is adding a negative voltage that helps with current flow. ...
You have a rubber band. With no stretch it's floppy. Apply enough stretch and it breaks. Let's say you stretch the rubber band to a mid-point between flop and breaking; that's "biasing the rubber band."
You do the same with your tubes. Except your "stretch" (negative bias voltage) turns down tube current from the breaking point (maximum current) closer to floppy (zero current).
So we adjust the bias to im assuming "divert" some of that extreme current elsewhere?
Remember positive & negative attract from grade school? The hot cathode emits negative electrons; the positive plate sucks the electrons out to the power supply. A course grid of spiral wire sits between the cathode & plate. If you apply no voltage to the grid, and the plate voltage is positive-enough, it sucks all the electrons emitted by the cathode through the wide gaps between grid-wires. If you apply a big-enough negative voltage to the grid, the electrostatic field created repels all the electrons back toward the cathode, and no plate current flows. If you set the negative grid voltage to some mid-point, the field retreats in closer to the individual grid wires, and some middle amount of electrons pass through unimpeded.
So current doesn't go somewhere else, it just sits back at the cathode and never goes anywhere.
So when I set the bias of my 2204 to 38mv, what is that 38 mv actually a measurement of? Is it the negative voltage that is applied to the tube?
Measuring voltage is easy with any meter. Measuring current is harder with most equipment, as you have to break the circuit, and situate the meter to complete the circuit so the current flows in/out of the meter.
If you install a 1Ω resistor between the tube cathode & ground, you can use Ohm's Law. Voltage = Current * Resistance; 38mA of current through a 1Ω resistor = 38mA * 1Ω = 38mV dropped across the resistor. Current through the resistor can be directly read as the voltage across the 1Ω resistor.
So "bias voltage" is the measure of the voltage difference from cathode to grid (almost always a negative number), while "bias current" or "idle plate current" is the tube current resulting from the application of the bias voltage. Some might refer to the voltage across the 1Ω resistor as "bias voltage" but that's technically wrong or at least misleading once you get to a point where you're really trying to understand how the amp works on a micro-level.
Topic: Quick question regarding my 2204 (Read 2932 times)