power selection switch, question/ choice.

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4/14/2000 4:58 AM

Bryan James

power selection switch, question/ choice. was looking at the marshall jcm900 schematic and noticed a switch that changes the input on the screen of the el34 from just after to the choke to in parrellel with the plate. the switch is labeled hi low.   is this the half output power switch?   can someone explain how it works?   and which would be better to put in a output section. (built from scratch, not moding) this high low switch or the 60/100 switch from mesa/boogie (the one that removes 2 of the tubes from ground.     -Bryan

 

4/14/2000 5:13 AM
DIRTY L KARLSSON	It´s a pentode/triode switch.     http://artists.mp3s.com/artists/74/slide_man.html

 

4/14/2000 2:19 PM
Bryan James	ah so that's what that looks like     so which would be better for reduceing wattage?   a pentode/triode switch of the boogie 60/100 switch?

 

4/14/2000 7:04 PM
Tonefactor	quote: "so which would be better for reduceing wattage?   a pentode/triode switch of the boogie 60/100 switch?"     The easiest and best sounding IMO, is to add a switch which disconnects two of the ouput tubes cathodes, effectively cutting output power in half.

 

4/14/2000 9:29 PM
Bryan James	The easiest and best sounding IMO, is to add a switch which disconnects two of the ouput tubes cathodes, effectively cutting output power in half.     cool that's what i was planning on doing but when i saw the pentode/triode switch i want hmmmmmmm i wonder     Bryan

 

4/14/2000 9:48 PM

steveR

Half power only results in a moderate reduction of perceived volume. I've found there is more actual volume reduction with a p/t switch. However triode mode is darker, sounding somewhat muted. But this may be good if you're going high gain crunchiness. Triode mode will also tend to have a bit more hum.     Heck if you're building from scratch why not do em both and make the decision with the guitar in your hand instead of the soldering iron.     Also, if you are going to shut off two tubes and you're using cathode bias, it might be a good idea to have a cathode resistor for each tube or each push-pull pair. That way when you shut off two of them your bias won't go way outta wack.     steveR

 

4/14/2000 11:15 PM
DIRTY L KARLSSON	Good point there !   Whith separate cathode resistors.   And the separate triode and quartet/pair switch.   No bias outta wack.   I´l try it out on my new PROJECT.   A mix of a Matchless CHIEF and home drawn dessign.     I´l let you know how it works out.     DIRTY L KARLSSON   http://artists.mp3s.com/artists/74/slide_man.html

 

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