TUBE BIAS, socket to me!

I suggest you buy an elementary treatise on how vacuum tubes operate, and then read it. In the accepted model for a vacuum tube, electrons are emitted from the cathode when it is heated. The cathode accumulates electrons and hence is thought of as having a negative charge. Because the anode is positively charged, or relatively deficient in electrons, they flow cathode to anode. If this is all that happened then vacuum tubes would be like light bulbs; the cathode would give up electrons in an uncontrolled manner, and they would flow to the anode. When this process reaches a state of equilibrium, the tube would be burned out and that would be the end of it. But instead there is a "grid". The grid is situated in the path of the electrons on their way to the anode. In a functioning tube, most of the time, the grid carries a net negative charge with respect to the cathode, and thus retards the rate at which electrons get all the way to the anode. That is, when no music signal is present, the grid has a DC voltage on it that is negative with respect to the DC voltage on the cathode. When a music signal is present, think of that as an AC voltage, a voltage that varies with frequency and in magnitude and represents music. So, music enters via the grid which always has a constant DC bias voltage on it, in simplest terms. The music signal modulates the grid bias voltage, and in another story, that’s how we get amplification of the signal across a resistor that connects the anode to the PS voltage. When amplifiers talk about "bias", they are usually referring to this steady state DC voltage on the grid. That grid bias voltage also results in a steady state current (electrons) passing from cathode to anode when there is no music signal. This DC current is referred to as "bias current". The grid bias voltage, the "plate resistance" of the tube, and the power supply voltage between anode and cathode, also called the "plate voltage" together determine the bias current. (Ohm’s Law.) For any power tube, or any tube at all, you can usually find a complex graph depicting "plate curves". This single graph will show current on the Y axis and plate voltage on the X axis, and a set of curves depicting what that tube will do at different acceptable grid bias voltages for different changes in plate voltage or current. And....

In his Music Reference section of the AudioCircle Forums, Roger Modjeski provided lots of info about tubes, including their biasing. Those writings are still available for viewing.

ya and Roger.  M ( rip genius ) spent man years.....wait for it....building MUCH better tube testers....

Elliott, your 110z is a treasure, enjoy it in good health

My Cayin is A88T version 1, which has 16 ohm taps for my 16 ohm speakers.

It has no external bias adjuster, no bias meter, and no switch for tube type.

Later versions drop 16 ohm tap, add external bias and bias meter.

So, it’s bottom off, multi-meter alligator clips, screw driver, ON, electrocution or success!

@oldhvymec, the old Hickok testers and the like tested MUTUAL CONDUCTANCE at low voltages, not at the operating voltages that they were likely to see. Makes a huge difference.
Would you pressure test a gas cylinder that routinely is filled with hydrogen at 2000 lbs by checking it with only 500lbs of pressure? Of course not, wouldn't even dream of it.
So why would you test a vacuum tube that runs at 450 VDC plate voltage with 100VDC or less. Sure, it can tell you that the tube is conducting but not how well it will conduct under a real load. That's best left to either testing in the actual amplifier or a modern tube tester like a Amplitrex AT1000 that can put up to 500VDC and 160 milliamps on the plates. There is another modern tube tester that sells in kit form that can test to much higher voltages as well. Both of these testers tie into a laptop computer and can plot curves for the tube under test. THAT's the kind of tester that can match tubes, not the older ones. Neither is cheap, I'd love to have one myself.
Not saying that the older tube testers are worthless by any means, they can be used for testing shorts (very important), gassy tubes and microphonics along with a doing life checks and basic health. But to match up tubes? NOT. That is best done either with one of the advanced testers or in the amplifier itself and a test meter. Anyone telling you different is either ignorant or trying to get over you. The best tube sellers today are using the latest test gear, the old TV7 type tube testers were the shitt years ago but old tech today. Times have changed my friend and this new tube testing technology is awesome.

BillWojo