ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

previous: dale my marshall jubilee has a triode/pe... -- 5/2/2000 9:48 PM

Re: 1/2 power switch question

5/2/2000 10:53 PM
Ray Ivers	Re: 1/2 power switch question Dale, 1) I believe the current thru the tube will increase when triode mode is selected - how much I don't know, I imagine it's different for almost every tube type. I would think that the normal plate-dissipation bias 'rules-of-thumb', if those are what you go by, will work in either mode. My experience has been that to maintain the same current flow thru the tube in triode mode as in pentode, the negative grid bias voltage must be increased. If you are going to use it mostly in triode mode, then, it might be best to bias it in that mode of operation. See what your current draw is in both modes, and go from there. 2) It could be a small factor, but the main factor reducing treble response is the great increase in grid-plate capacitance once you've lost the shielding effect of the screen grid. Triode amps designed as such from the beginning take this into account when designing the driver stage (you need considerably more drive voltage for a triode stage, too), whereas most guitar amps don't seem to. Ray

5/2/2000 10:53 PM

Ray Ivers

Re: 1/2 power switch question

Dale,

1) I believe the current thru the tube will increase when triode mode is selected - how much I don't know, I imagine it's different for almost every tube type. I would think that the normal plate-dissipation bias 'rules-of-thumb', if those are what you go by, will work in either mode. My experience has been that to maintain the same current flow thru the tube in triode mode as in pentode, the negative grid bias voltage must be increased. If you are going to use it mostly in triode mode, then, it might be best to bias it in that mode of operation. See what your current draw is in both modes, and go from there.

2) It could be a small factor, but the main factor reducing treble response is the great increase in grid-plate capacitance once you've lost the shielding effect of the screen grid. Triode amps designed as such from the beginning take this into account when designing the driver stage (you need considerably more drive voltage for a triode stage, too), whereas most guitar amps don't seem to.

Ray

Replies:

dale Thanks Ray ! -- 5/4/2000 5:43 AM
kg Re: 1/2 power switch question -- 5/4/2000 1:39 PM