Why is there so much difference in wattage ratings between amps? I'm just curious.
I've been playing for years with many amps that use 6L6 tubes for example. Some 6L6 tubes are 25w but most are 30w. So let's just assume we were using AB type amps ... Why wouldn't wattage be:
(2) 6L6 = 30 watts
(4) 6L6 = 60 watts
I know I've seen ratings for (2) 6L6 tubes at 25w, 33w, 40w, 50w, 60w
What makes them different? Is it just different ways to measure? Is it differernt output transformers? Is it the way you treat clean vs distortion in the calculation?
Basically, if I pull the same (2) 6L6s out of any of these amps and put it into another, won't they be close to the same loudness?
Just curious ... I know it's not a hugely important thing but I just started wondering.
Calculating wattage ratings on tube amps?
Moderators: pompeiisneaks, Colossal
Re: Calculating wattage ratings on tube amps?
It totally depends on the voltage applied to the anode and the way the tubes are biased - fixed (adjustable) vs cathode biased.
Take a look here:
http://tdsl.duncanamps.com/show.php?des=6L6GC
The Va column is anode voltage and the Pout is power out. Just look at the huge difference between AB1 and AB2 push-pull voltages and output. Also look at the class A Push-Pull differences with the different Rk values that are listed... So a pair of 6L6GC's could produce anywhere from 18.5 to 72 watts just depending on these factors.
Take a look here:
http://tdsl.duncanamps.com/show.php?des=6L6GC
The Va column is anode voltage and the Pout is power out. Just look at the huge difference between AB1 and AB2 push-pull voltages and output. Also look at the class A Push-Pull differences with the different Rk values that are listed... So a pair of 6L6GC's could produce anywhere from 18.5 to 72 watts just depending on these factors.
Re: Calculating wattage ratings on tube amps?
It is my understanding that along with voltage it also depends on the Ra of the OT. For the pp circuits on the duncanamps page, the OT is 1700 Ra. An OT with a different Ra would yield a different result. The Ra will determine the current draw of the tube and hence the Pwr at that particular voltage. See KOCs tut series. There's sure to be other texts on it though. 
Dunno about the pt of bias changing pwr, certainly not in any significant way. The duncanamps page given shows no evidence to support that idea. As long as you've got the same bias pt (whatever method) the pwr should be similar but the amp will sound sonically different. I'm prepared to be corrected though.
Brown.
Dunno about the pt of bias changing pwr, certainly not in any significant way. The duncanamps page given shows no evidence to support that idea. As long as you've got the same bias pt (whatever method) the pwr should be similar but the amp will sound sonically different. I'm prepared to be corrected though.
Brown.