JLeurck

Originally posted by Duke of Metal hey Scott, You can use EL34s in the T100 for sure. I use JJ E34Ls in mine. I sorta suggest changing the Screen grid resistors to 1k/5w. I did that with mine just to make sure i can use different types of power tubes safely. Its adjustable bias. If you open the top panel to the opposite side where the tubes mount, you'll see 2 blue trimpots. each channel gets biased seperately. If your cab is 16ohms and you want to use it in mono 100watts, set each channel to 8 ohms, which equals a total of 16ohms. Here's a website to a pdf manual and schematic I scanned for the owner of that website: http://www.glowingtubes.com/p/amplification.htm Hope that helps Cheers Awesome site! Does your Quad-X have the MIDI in-out on it? Mine is an older one that advertises MIDI capability, but since it isn't a latching switch for the channel selection, it is a no-go trying to use a CGX and a Ground Control (or anything else, as best I can tell). I jsut cannot figure out how to get this thing to channel switch and patch switch via MIDI at the same time. Nowadays I mostly use it to record clean parts at home, but I did find that frustrating, for sure. P.S. I've got Rev 1.1 of that T100 manual that shows in the cut-away illustration right where the bias pots are (manual No. 96-10101 / June 1994). I'd like to try the EL34's in there myself, but am perfectly happy with this tubed with 5881s (though I'm generally an EL34 guy from the Marshall camp). Great power amp - just wish the damned presense controls were on the front!

That 50ma figure is straight out of the manual. Did you find the bias pots? Maybe they mean not to exceed 50ma? They are pretty specific with that 50ma figure. Here's the paragraph verbatim from the manual: ".....For qualified technicians only. Remove 'Red' output transformer leads from QC11 & QC12. Measure the current between each red lead and the connector. Adjust each bias trim pot for 50ma. See Tube 100 Specifications......." From the specs page: ".....The internal BIAS adjustmemts (2) must be re-set when changing from 5881 to EL34 power tubes (also recommended for replacement of new tubes of the same type). To properly measure this, disconnect the RED center tap lead from each output transformer (connectors QC11 and QC12 - one at a time) and take the DC current measurement (50ma each) between the RED lead and connector. Because of the dangerously high voltage (500 V), use only a qualifierd technician to do this procedure. If the Bias is not properly set, crossover distortion and overheating will result......." I'm not a tech, but this figure does seem high. My 5881-valved Holland is set for 35ma. Maybe shoot for 35ma like others have suggested here. Like I said, I don't have a scanner here. If you PM me your address I can photocopy the manual and send it to you. It's only 12 pages.

If you have the top off the amp with the volume knobs facing you and the speaker jacks facing away from you, you will see a vertical metal plate that separates the tubes/transformers from the front 1/3 of the amp. On that metal plate is something that looks like the plug to a two-pronged power cord (on the top of the metal plate with the prongs again facing the front of the amp). If you look down diagonally from that prong looking thing, to both the left and right on the bottom front of that metal plate you should find two bias trim pots - one for each stereo side.

I've got one of these but mine came w/5881s. The manual says it will take either but you need to reset the bias or you will damage the amp (there are bias trim pots for each stereo side - it says set the bias for 50 milliamps no matter which tube is used). As for the bridged mono thing, the min load it can take is 8 Ohms. Set each side for 4 Ohms for an 8 Ohm mono load, each side to 8 Ohms for a 16 Ohm mono load. No provision for a 4 Ohm mono load.