Casey4s

I don't bias with a calulator. I use a scope and I measure idle current after that. Published tube ratings are a "safe" zone that the manufactures used to prevent premature failures. It's not real world. The calculator method sorry to say is for the DYI nOObs, you must make sure you figure in screen dissipation too if you're going to try this:idea: Also, one more tid bit; Make sure you're measuring unloaded voltage if you use a calculator, that means pull your tubes before you do anything. Any easier way, and if you really want to set it up as the manufacturer/fender did, look at a schematic, it shows the loaded voltages for the output stage. Bias it until the voltage matches the drawing specs. Then go back and see how much current you're drawing. You might be surprized. Don't get defensive Doug, I did not say you were wrong or misinformed. I have a Tektronix scope here and most of the time it has been my personal expierience when biasing with a scope to the crossover, the actual measured ma is pretty close to the math. I was under the impression that the OP was not using a scope so I used the recommended math from an RCA manual to recommend a ball park figure for him. Most of the DIY n00bs don't have a scope or even know how to use one so the matamatical calculation works well enough most of the time and was the standard method before there were scopes in common use. Don't be too hard on the DIY n00bs Doug, they are trying to learn somethihng.

35-40 ma per tube. have a nice day. 40 ma is only about 60% of the max in this instance which is fine but a little cool for my taste. If this were my am I would probably bias at 65% or maybe 70%, but it's all a matter of personal taste as to how the amp sounds to the owner and how much longevity they want to get from the tubes.

I think your math is off. The amp's maximum output is 85 watts. You calculate the 70% off of that. Your math is off Sir because 70% of the total of the four 6L6GC's IS 84 (85) watts. You are getting 70% of 70%. The amp is rated at at 85 watts because that IS what 70% of four 6L6GCs comes to.

30 watts per tube x4=120watts. The twin reverb is NOT a 120 watt amp and there's your problem. 445V times .047 amps is 21 watts times four tubes is 85 watts. If you have the current at 47 mA then you have the bias set at 100% dissipation at idle. Way too high.. You want to set the bias at 65% to 70% of that figure....Maybe 31mA or there about. 120 X .70 = 84, which is about what that amp is rated at. OR 30 X .70 = 21, for one tube. 31 MA in this case is only about 47% Nobody has claimed that this amp is a 120 watt amp, you must have misread something. No AB PP amp is rated at the actual addition of it's power tube maximum disipation, a 2xEL34 amp at 70% is actually a 35 watt amp not the 50 watts of the two 25 watt EL34 tubes.

I just got 4 JJ 6L6GCs for my Twin Reverb. I've done biasing before. What bias current do I want for my 6L6GC power tubes with the Twin Rever? The Weber bias calculator*, at 445 measured plate volts, suggested 47 mA but my amp wont let me go above 45 mA. The Weber site assumes the power is 30W for the tube. Since the Twin reverb is rated at 85W, do I want to divide 85 watts / 4 = 21.25 W for the wattage for each tube, divide 21.25 number by 445 and then multiply by .7? This gives me 33mA. http://www.webervst.com/tubes/calcbias.htm If you bias at 65% I get 43ma (43.8) per tube with a PV of 445. You could go a little cooler but I think you'll like it better at 65%. [Divide the 30W for the 6L6GC by the 445 PV, then multiply by .65 to get the 43.8.]

Originally posted by televisionary Wouldn't it rock if Guitar Center or wherever, tested you before you could buy the high end gear? They had a panel of musicians (albeit dead end ones, considering they work at GC) that critiqued your playing, and based on your score, you get to buy a Crate and a Squire, or a Les Paul and a Triple Rectifier. If the Sonic Youth type guys liked your playing, they'd let you buy a Jazzmaster and a Vox. So just what do you see yourself playing under those rules? Then they should decide at the DMV what kind of car you were allowed to own based on your driving test. Just made it guys would be driving used Yugos and top qualifiers could own Ferraris or Porsches. Bob has the right answer if your wallet qualifys you that is all that's needed. It is about MONEY and nothing to do with talent.

That's kind of a stupid question. What qualifications other than $$$ do you need? Do your driving skills justify the car you drive? Do your {censored}ing skills justify the {censored} you get? Etc etc etc. :D :D