Biasing question & Comment etc.

[yardbird mac]

How many here bias their own amps/tubes, and how hot do YOU bias & why... just askin'

I biased both of my Pro Tube Pro Reverbs a little hotter today. I realize this shortens tube life, but I think I like the subtle change I'm hearing... dare I say "warmer".

I also reinstalled my original JENSEN C12Ns in both amps. The EMINENCE Cannabis Rex's I had in them ended up not fitting my style of playing. Don't get me wrong, I think these are speakers (the CRs), but I like the "harder" "tighter" bottom end of the C12Ns.

 

[VanR]

between 60-65% usually

 

[marsos52]

i bias my amps and most of my friends amps..

i used to bias on the hot side.. a year or so ago i tired biasing my amps (1 with el34's and 1 with 6l6's) on the cold side...i didnt like the amps on the cold side they seemed to loose something ....it seemed lifeless to me even when cranked..

i generally go for medium to hot but i use my ears ...listen to the amp idle and if its not noisey i am close...play it a while and see how it sounds and re-acts.. after a few weeks i check the bias to make sure it has not changed.. if the amp starts to be noisey and the tone is changed i just check the bias again

so thats what i do ,,,works for me

 

[skynyrd]

Most 6L6 tubes have a max Ma rating of 30-35 correct?

 

[Joe Porto]

Most 6L6 tubes have a max Ma rating of 30-35 correct?

30 watts for 6L6GC in class A/B according to RCA tube manual. That would be a maximum idle wattage of 21 watts (70%).

 

[riffmeister]

Most 6L6 tubes have a max Ma rating of 30-35 correct?

depends on the plate voltages......lower voltages mean you can go higher on the bias current and vice versa.

Here's the arithmetic for a 25 watt tube with 450 volts on the plates biased to 70% dissipation:

(25 x 0.7)/450 = 39 mA

 

[Rick0]

I always bias when I change power tubes, (unless cathode biased). I like 6L6GC's to be at 32 mA each. I think this sounds best for my TR's. I use NOS and want them to last a while.

 

[Joe Porto]

As Riffmeister said, mA settings mean nothing without knowing the plate voltage. It's all about wattage.

 

[Fuchsaudio]

http://www.webervst.com/tubes1/calcbias.htm

Check it here.

 

[yardbird mac]

Thanks!!! I looked at that table. My Pro Tube Pro Reverbs read somewhere between 425 - 450 V. According to the table on this site, then, I can safely run them at 43 mA without causing any circuit damage (other than shortening the tube life)...???

 

[jamesrsmith]

i bias my amps that arent cathode, i finally got wise and got a bias probe. there are no amp techs around here for 150 miles.

 

[mad dog]

I bias my own. I guess the general range for me is 65 to 70 percent, but it depends not only on the amp and the voltage, but on the tube. Some tubes sound better a little hotter. Others don't. On the cold side never seems to work.
MD

 

[Fuchsaudio]

Thanks!!! I looked at that table. My Pro Tube Pro Reverbs read somewhere between 425 - 450 V. According to the table on this site, then, I can safely run them at 43 mA without causing any circuit damage (other than shortening the tube life)...???

It comes down to current tube quality, and how long you'd like things to last. We run about 500 on 4 6L6's in our 100's with TAD shorties, and 36 ma seems to be the best balance of tone and tube life. If the tubes were Sylvania STR's I'd say "blast away"...alas, we don't know how good todays tubes are until they show us by failing....