PLEASE PLEASE PLEASE!!!! READ THIS NOTE:
We say that you can go as high as 90mv at the test points for the JJ 6L6GC's. This DOES NOT mean that it HAS to be set at 90mv!!!!!! PLEASE read below!!!!
We get phone calls and emails everyday asking why the bias has to be set at 90mV and the most asked question is "I can't get my bias to 90mV now what do I do?" Or "I set my bias at 90mV like you said and it distorts too early".
At the risk of sounding like your third grade teacher (or at least what my third grade teacher sounded like) LISTEN UP AND OPEN YOU EARS AND EYES PEOPLE! As I state in the video, you DO NOT have to set your bias at 90mV!! We consider anywhere between 70mV up to 90mV a usable range with 70mV providing more headroom and 90mV providing an earlier breakup. Some HRD's will not quite hit 90mV depending on the value of the final bias resistor and or pot. This does NOT mean your amp is broken!! the value of the components will vary.
YOU DO NOT NEED BIAS PROBES TO BIAS THESE AMPS! YOU CAN USE THEM BUT THEY ARE NOT NECESSARY. A SIMPLE MULTIMETER IS ALL YOU NEED!!
The second most asked question that we get is "what do I set my multimeter to?" If you're using the test points as shown in the video then you are measuring millivolts. Millivolts can only be measured when the multimeter is set to DC volts and we recommend a 200 millivolt scale.
This video is of a Hotrod Deville which has a little higher plate voltage than the Deluxe but the bias recommendations at the test points are just fine for both the Deville and the Deluxe. If you're after maximum headroom then set the bias to about 70mv. If you're after an earlier breakup you can go as high as 90mv. Remember there is no right, wrong or "perfect" bias setting within this range. It's where YOU like it best. I simply want you to have the knowledge to be in control of your tone! Try different settings to see what works best for you.
A word of caution!!! Other brands of 6L6's like the chinese tad tubes and sovtek, Svetlana, EH, and the new tung-sol tubes are ALL sovtek tubes and cannot dissipate as much power as the JJ's so I don't recommend running these any hotter than about 75 to 80 and the gt 6L6ge should not be set higher than 70 or you will burn them up VERY quickly!
These amps vary so not all HRD's will be able to hit 90mv at the test points and if you ask us for power tubes with good headroom we will send a more moderate grade and sometimes these will top out at 75 to 80mv but if its headroom you're after then that is a good place to bias the amp.
A note to JJ 6V6 users; The JJ 6V6's can be biased as high as 45mv at the test points in Hotrod Deluxe's but most of these amps will only hit about 30mv but even at this setting they sound great. If you want to really push them then you need to drop the value of the final bias resister down by about 20%. A bias setting between 30 to 45 is best for the JJ 6V6's.
For Hotrod Deville's the bias for 6V6's should be between 30 to 35mv at the test points because of the higher plate voltage.
The red or positive test lead is the one you want to touch off to the test point shown in the video and in the pic's below. The black lead can simply rest in one of the screw holes on the chassis (very handy) or touch off anywhere on the chassis.