Tweet
Could somebody explain to me how a 35Watt EL34, class AB push pull output amp with a plate to plate Z of 3.4K, a 375V anode supply, and cathode bias resistor of 130 ohms (or two 270 ohm- one per tube) running in a quiescent state of 75mA per tube, be running safely within it's 25 Watt limitation. I got the data from the "Miniwatt tech data book". This output section seems similar to some of the Badcat or Matchless range and obviously works, but 75mA and 375Volts seems to be more like 28Watts. Maybe I've missed something. Any help would be much appreciated.
-
-
Screen current. -
i believe you would have to measure the voltage from the anode to the cathode, not anode to ground. the cathode resistor is dropping some of the voltage as well. there is most likely more to it. i dont think about calculating power.Comment
-
Safe power range for EL34 etc....
Further to what I mentioned earlier, the 75mA was purely to each anode. There is a further 11.5mA screen current per tube, totalling 86.5mA, per tube (total 173mA)through the 130 ohm cathode resistor.There should be 22.5V at the cathode.Subtracting that from the 375V at the anode gives 352.5V multiplied by 75mA gives 26.4 Watts. The 26.4Watts power at idle is at the limit of the tubes capabilities. So is it O.K. to run like this? Maybe the limitations put on the tubes by the manufacturer do not reflect the true capabilities of these tubes. I appreciate your answers. I've been building tube guitar amps for some time now, but there's always more to learn.Comment
-
As I have said many times,the specs you see in tube manuals dont always reflect what we do to tubes in guitar amp applications.Most of the data you see was written before guitarists started abusing tubes.As Enzo has pointed out,they were written more for radio and TV applications and for longest life in such applications.You will see Hi-Fi guys adhering to these specs since they want pure,clean music reproduction with the least distortion possible,for us even when we operate the amp for a "clean sound" a little distortion is more desireable.Comment
-
As the measurement of cathode current is the sum of anode and screen dissipation, the limiting values are 25W for the anode, and 8W for the screen; so in this application it is within safe limits.Comment
-
Thanks.
Thanks for all your help.It's good to meet such an enthusiastic bunch of people online.Comment
Comment