Question on Tube Swapping and Biasing

“Multimeters are really cheap” - yeah, kind of! LOL

Cheap DMMs are really cheap, and results are not accurate or predictable, due to many factors, such as RFI impact, sampling rate etc.! I have couple of Agilent/Keithley bench DMMs in my Lab, $5000+ each, and I use them for sensitive circuit tuning!

Before adjusting bias current by measuring amp’s internal resistor’s IR voltage drop, would be appropriate to test resistor(s) value itself first, which could be easily 20%+ off schematic.

@westcoastaudiophile Please! The average audiophile has to believe in something! As I stated earlier, bias is a moving target (see quote below) and is not something anyone needs to obsess about! People in the know will state quite frankly that there is no "last word" regarding bias. The most you ever need to do is maybe check it once or twice when the amp is new after a good warm up and make sure the bias isn't exceedingly high for any one tube then you can rely on the set of tubes the MFG included with the amp and maybe, maybe check it once a year. The bias at any one time can be 25% below the nominal and not have any significant effect on the sound the amp produces or any damaging effect on tube life. Check it again the next day and it may be within a few percent of the nominal spec for that amp.

"“Multimeters are really cheap” - yeah, kind of! LOL

Cheap DMMs are really cheap, and results are not accurate or predictable, due to many factors, such as RFI impact, sampling rate etc.! I have couple of Agilent/Keithley bench DMMs in my Lab, $5000+ each, and I use them for sensitive circuit tuning! Before adjusting bias current by measuring amp’s internal resistor’s IR voltage drop, would be appropriate to test resistor(s) value itself first, which could be easily 20%+ off schematic."

My comments from up thread. -

"FYI, bias is a moving target. Knock your brains out trying to get it right on the money then blink. In theory a matched quad is all you all you need to do but the primary caution is not having a single tube or tubes drawing significantly more current than any of the others. Other than that, the bias is likely to be all over the place at anyone given instant and is nothing anyone with a tube amp should ever obsess over.

Your JJs are probably still just fine and unless you have any particular indication that things are not as they should be, you should leave them alone."

Thanks all for the interesting discussion! I bought a multi meter and insulated screwdrivers, but am waiting to tweak the bias until after I return from a trip. 

In the meantime, I've switched out the Luxman tube amp for a Benchmark AHB2 Power Amp I use in my "Summer System." I have to say, it sounds really great with the CL-38use preamp. Not a combo I would have thought would work, but there you go. 

Finally getting around to biasing my amp. But the more I read the more confusing it seems:

The amp is supposed to be hooked up to speakers and on for an hour before biasing. However I’ve also read that you should discharge the electrical charge before starting. How is that possible? 

Are you supposed to be playing music during the biasing? 

Where to set the volume control during biasing? Bass, treble, etc? 

What other "obvious" things am I missing? 

Thanks for any insights!