TUBE BIAS, socket to me!

How about a long carbon fiber tube screwdriver!!!

I'm gonna find something long enough n my shop, use my grinder to make a screwdriver tip, have at it.

Elliott, if it has those tiny little pots they make adjusting tools for that. I always called them "tweakers" LOL, Radio Shack sold a set of 3 for just a couple of bucks, made of plastic.
If your going to do this, just make sure that the power is off when you attach your insulated clip leads. Use your meter set to DCV and check the PS caps to see how long it takes them to bleed down. Most PS have a bleeder resistor across the caps that will discharge the high voltage in just a few minutes.
Not a bad idea making an insulated tool, easy to slip and make sparks/do damage.
I bet Greenwood has the proper tools, do I really need to give YOU an excuse to go over there? LOL.
BillWojo

Bill discovered this, near me, it's Toyland to him

Greenbrook Electronics, filled with vintage as well as new stuff!

https://www.greenbrookelectronics.com/

I'll be standing on an AstroTurf rug I have at my workbench, nearly 2" thick plastic and rubber, concrete below.

OFF; no inputs; multi tester connections; ON; 20 min warm up; long plastic tool. OFF, disconnect.

Speakers connected?

thanks for providing that understanding, big help just knowing 'why' bias exists.

Is it fair to say, if it sounds great, don't mess with it, or why bother as some suggest?

Thanks and yes, if it ain't broke don't fix it. 

Technically, the bias setting really does make a difference. In practice however it is like an oil change, you will always swear it makes the car run better. 

By the way, the same concept of bias is used in tape recording. The little particles in the layer we want to magnetize to record on, they don't respond very well if all we do is feed them the audio frequency signal. They are kinda slow when asked to change from zero state. But if we excite them with a bias current, in this case 60kHz or higher, this puts them in a state where they respond much better to the music signal. Very similar or analogous to tube bias.  

Mine one time somehow got way out of spec, something like 2 or 3 times what it should be, and so I was anticipating this nice improvement after spending the few minutes to lug out the meter, get down on the floor twiddling and testing to dial them all in nice and perfect. And then... nuttin. Nada. Oh well. At least the car runs better now.

Elliot, I am not quite sure I understand your question, "Sonically, what are your experiences?"  Do I think biasing an output tube makes a difference?  That goes without saying; a power tube cannot operate without some chosen parameters: plate voltage, plate and/or cathode resistor values, grid bias, etc, that determine the electronic envelope in which the tube operates.  For every tube, there is a data sheet, usually available on-line and/or in published tube manuals.  These data show maxima and minima for plate voltage, bias, plate current, etc.  The tube has to be set up so its operation falls within these upper and lower limits.  And taken with the plate curves I mentioned earlier, you can "see" how different choices within that envelope of values will affect performance when the tube is fed an audio (AC) signal that will have a voltage swing.  I use exclusively Atma-sphere OTL power amplifiers, so of course no output transformer, and the power tubes are triodes.  In fact, in 45 years, I have never owned a transformer coupled tube amp, only OTLs driving ESL speakers. With Ralph's help, I built my amplifiers so I can set bias current for each of the output tubes separately.  This allows me to "match" the tubes for the way they are treated by the circuit.  But tubes themselves are unavoidably at least slightly heterogeneous in the way they individually respond to signal voltage.

If you consult with tube gurus, many of them have their own pet theories on where to set bias points for various power tubes, for best SQ and/or for most power, longest life, etc.  (Sometimes the settings for best SQ conflict with maximizing tube life.) By the way, the description of vacuum tube operation in my previous post is for triodes only.  So called because there are 3 nodes, plate, cathode, and grid.  Hence a "tri"-ode, the simplest type of audio tube.  Most power output tubes especially on transformer coupled tube amps, will be tetrodes or pentodes.  The extra nodes are additional grids that can further control the flow of electrons to the anode, but only the one grid receives the signal (with some very rare exceptions; for example some Berning amplifiers drive the screen grid); normally the one or two screen grids do some of the modulating of electron flow by virtue of the voltage supplied to them.  Small signal input tubes and phono and linestage tubes are nearly always triodes.