post #1 of 1
Thread Starter 

I always get a little frustrated reading reviews and suggestion on NOS tubes based on limited experience with tubes. It first needs to be understood that there are huge variances in tolerance, even with the same brand.  This applies to all tube new, used, and NOS.  The reality, is that most tubes sold on eBay are limited in their testing.  The 3 major factors effecting tone are:

 

1. gain

2. transconductance

3. plate resistance/bias/current draw

 

To simply say that a specific brand is better, simply means it sounds better that the other tubes in you possession.  You can buy the most expensive and revered tube out that is only 75% in spec, may not sound better than that a chinese tube in spec.  These things are typically ignored by most rollers.   

 

Most tubes sold on eBay are only testing in either only gain or only transconductance, rarely both.  If you truly want to evaluate tubes, find a reputable vendor that you can build a relationship with and get various brands that all test within similar specs.  Otherwise, you are simply not giving tubes a fair comparison.  I am not exaggerating the huge variances in tubes new and old. At a minumum make sure you tubes are comparable in both gain and transconductance.  If you are running power tubes in a push/pull design, you need to make sure they are matched for current draw as well.