If the OT is a Hammond, it already has more bandwidth than you need and passes the extra power without you noticing. So let's guess that you might bias a bit cooler and under heavy drive you get a bit more than 25w. PRR alluded that even a cathode-bias amp may be run as a hot class AB amp. Regardless, a true class A E元4 amp won't do more than 25w and will likely do noticeably less. OT's usually aren't specified in VA, but maybe that's just showing your preference for that term. I'm not PRR, but here's my take: first guess, yes it will be fine. That's what hours of experimental work can do, better than cut-and-try or napkin calulations. This heavy load and loose distortion spec allows current consumption to rise 26% from idle to roar, efficiency touches 49%, so power output is more than half the idle Pdiss. I _suspect_ there is a typo on this sheet: 'Va+Vrk' should be 'Va -Vrk'? So 350-400V, 3k4 to 4k load, cathode resistor near 130 ohms (start above 150 ohms and work down). E元4 data page 5 shows cathode-bias 'AB' conditions for E元4.

Total supply can be 316V+30V or 346V.īut why guess? Back in 1956 people were paid to *sell* these tubes, by making it easy to design-in to equipment. Cathode bias drop is likely to be near Vg2/ Mu or 300/10 or 30V. So we want a 2K load on the supply, and suck 50 Watts idle power consumption. I can testify that 395V, 200 ohm Rk, large Rs, around 120mA, 6,600 ohms load, gives in excess of 17W clean and happy. The push-pull plate-to-plate load should be around twice that, 6,400 ohms. Since efficiency will not exceed 50%, we already know power-out will be around 25 Watts. > pick one up that would give me around 400 Volts

So either you run a lower supply voltage, or a higher impedance. The idle current can be small power consumption will rise with signal.Ĭathode-bias, the idle current and power consumption *must* be nearly as high as the full-roar power consumption. I had no idea i would use anything differant than standard marshall style 3.3 k

Cathode bias guitar amp