software

I know that Pentode is for the 100w setting on my amp and the triode mode is for 50w. I wondering if any of you know if putting on one setting wears the tubes down faster and if all tubes are working in both modes. Oh I forgot add if I can change between the modes while the amp is on? I got a marshall 2100 slx 100w, so you guys know what amp I'm talking about.

i would at least put it in stand by before switching modes.

Pentode and triode modes are pretty much fancy names for quot;full wattsquot; or quot;half wattsquot;. It is accomplished by taking out either the inner pair of tubes or outer pair. I recommend that you change the ohm cabinet settings as you do this. If you're going to cut the power in half, change from (if you're) 16 to say 8, or if you're 8 then change it to 4 ohms... etc.

Bear in mind, just because the watts is cut in half doesn't mean the volume is cut in half as well. You will notice a different type of breakup and tone in triode as well (just to let you know that it's normal).

I wouldn't recommend switching the power selection while the amp is on. I don't know if it'd cause any damage, but changing the circuit like that with live voltage can't be doing anything positive for the amp.

Actually, pentode/triode isn't referring to disabling some of the power tubes. Most power tubes run as pentodes, which are just improved triodes. This improvement in operation allows pentodes to get a much higher amplification factor than its predecessors. The screen grid is one of the electrodes that make the pentode so much more efficient than a triode. By connecting the screen grid to the plate, we can force our power tubes to run as triodes. Once disabled, the pentode suddenly doesn't have as much gain, hence a drop in perceived volume.

Thus, it shouldn't wear the tubes out faster, and all tubes are still working. But it will sound different. As triodes aren't very efficient at amplification, they don't amplify the high frequencies as much. That's the whole purpose of the screen grid; to improve efficiency and thus high frequency amplification. This causes a sort of muffled sound. FWIW, YMMV, etc.

Edit: Though this causes an impedance mismatch as well since the tubes aren't running as efficiently or putting out as much power. Less power, lower current:voltage ratio, lower resistance.


Originally Posted by Jag513Actually, pentode/triode isn't referring to disabling some of the power tubes. Most power tubes run as pentodes, which are just improved triodes. This improvement in operation allows pentodes to get a much higher amplification factor than its predecessors. The screen grid is one of the electrodes that make the pentode so much more efficient than a triode. By connecting the screen grid to the plate, we can force our power tubes to run as triodes. Once disabled, the pentode suddenly doesn't have as much gain, hence a drop in perceived volume.

Thus, it shouldn't wear the tubes out faster, and all tubes are still working. But it will sound different. As triodes aren't very efficient at amplification, they don't amplify the high frequencies as much. That's the whole purpose of the screen grid; to improve efficiency and thus high frequency amplification. This causes a sort of muffled sound. FWIW, YMMV, etc.

True, my VT-120 has is switchable 120w-60w AND has a triode/pentode setting.


Originally Posted by Jag513Actually, pentode/triode isn't referring to disabling some of the power tubes. Most power tubes run as pentodes, which are just improved triodes. This improvement in operation allows pentodes to get a much higher amplification factor than its predecessors. The screen grid is one of the electrodes that make the pentode so much more efficient than a triode. By connecting the screen grid to the plate, we can force our power tubes to run as triodes. Once disabled, the pentode suddenly doesn't have as much gain, hence a drop in perceived volume.

1.
My MarkIV has this feature.


Originally Posted by Jag513Edit: Though this causes an impedance mismatch as well since the tubes aren't running as efficiently or putting out as much power. Less power, lower current:voltage ratio, lower resistance.

If the impedance drops then is there a way for me to use my amp with my jcm900 1936 cabinet that runs 8ohms mono and 16ohms stereo, without getting a new cabinet. My amp head can only select 8 or 16ohms impedence.

Thanks for the guys