TUBE BIASING

[jcmusic]

What do you bias your SET 2a3 tube's to 500-600. Somewhere in the middle or something else. Or as high as you can get the two to match?

[mikebse2a3]

canyonman

If this is the ASL amp you list in your equipment I've not actually seen one so maybe someone that has will respond.

Is the 500 to 600 the manufacture's recommended setting?

My guess when you say 500 to 600 that the meter is probably reading a voltage drop across a reference resistor possibly of a 10 ohm value and the reading is actually 500mv to 600mv which if so then I=E/R would indicate 50ma to 60ma which seems to be a fairly common current setting for many B+ Voltages used in 2A3 amps.

Most of the orginal 2A3's are rated for a maximum Plate Dissipation of 15 watts although I believe some(maybe KR) of the more recent 2A3 designs can dissipate more.

Anway IMHO it would be best to stay within the range the manufacture gives you since that setting is based on the total amp's design(ie: Output Transformer, Power Supply, Etc....) unless you talk to the manufacture about Tubes being used that can take more current and they say the design is capable of long term use at higher current conditions.

Basically overbiasing the tubes will just overheat the tube and shorten it's life.

Slightly Underbiasing the tube will cause the amp to clip on peak signals most noticeably in the bass and vocal area of music. This shouldn't hurt the Tube but you want get the best sound with the Tube operating like that.

So if the manufacture gives you the range of 500 to 600 then I would listen at the 500 setting first and if it sounds as good as the 600 setting and you get the loudness you need at the 500 setting then use it because the tube will run slightly cooler and you should get the maximum life span from the tube. If the 500 setting doesn't meet your needs then start adjusting your settings upward till it does or till you reach the maximum suggestion of 600 set point.

mike[]

[3dzapper]

60mA is ASL's specification. That would be the 600 figure you cited. Set the bias as close to that reading as possible.

Too high and the tubes and power supply will be taxed. Too low will result in a loss of output power.

If you should get some NOS tubes that won't make the 60mA that modern 2A3s can, set them as high close to the specs that you can get. Set the stronger tube to maych theweaker one for balance.

If you want to try 45 tubes, set bias to 36mA (360) I've read.

Hope that helped.

Rick

[jcmusic]

Mike, thanks for your imput on the biasing, that was more informative than the owners manuel.

Rick, what would be the advantage if any going to a 45 tube, and can I do that without creating any problems for the amp? I almost forgot, I got some new sovteks, a matched pair.

Jay

[3dzapper]

Jay, I couldn't find a copy of the manual but in a thread on Audiokarma a poster was discussing ASL's recommendations in his manual. ASL says your amp can be used with either tube when properly adjusted.

The 45 should offer a more "delicate" presentation than the 2A3. This comes at a cost of one watt of power. If you have some, take a taste. It's free!!!![]

Rick

[jcmusic]

OK Rick, Thanks for the tip. I think I can get away with 1 watt of lost power, just wandering about the sound.

Jay