Combination cathode bias and fixed bias

[mooreamps]

Ahh, but you're describing your perceived benefits of PS, not it's ease of design/installation.

My power brake uses passive components, and only dissipates 2 watts in waste heat. No FETs, no fans, no heatsinks...... Benefits are real...

-g

[BackwardsBoB]

tubeswell - Now if you return to my post about the tremolo that confused you, I think you'll see how to keep the tremolo feature in place with a cathode biased solution. In the case of Hasserl's drawing, the wiper of the tremolo depth pot would go to where the pole (pin 2) of the switch goes in the drawing in place of the switch pole, and the the bottom of the depth pot would go to the pole (pin2) of the switch.

When you flip your switch, the .02uF blocking cap on the grid and any cap on the cathode resistor(s) will have to charge to a new voltage, and the bias voltage between the cathode and grid will be incorrect until this settles down. You could get a transient, which could be severe, through the tubes and the speakers. Whether the tubes turn off or the current surges is dependant on the final circuit.

[pete]

Take a look at Vox AC-50. Fixed bias and 47 ohm cathode resistor. Sounds good.

[mooreamps]

Take a look at Vox AC-50. Fixed bias and 47 ohm cathode resistor. Sounds good.

Yes, indeed it does... Now, certainly 47 ohms is not large enough for class A all by itself. But increasing it to a larger value would be for class A. Then just decrease the fixed bias voltage by the same amount for class A/B.

-g

[tubeswell]

THanks for the feedback everyone - very constructive and educational ! :-)