Once you know that, gradually turn the bias adjustment in that direction until the plates just begin to show some redplating. Increasing the draw will bring on a bigger, richer Sonic. Then, turn the bias pot a small bit and play it to find out which direction one should turn the pot to increase or decrease the current draw. All you need is the amp, a guitar and a tool to turn the bias pot. (PT tag says DE 4145, choke says drake t100 1471-263, cans are Daly's and OT is C272(?), last digit isn't legible.Okay, I’ll suggest the easiest way to bias an amp.since biasing without knowing the plate voltage is about the same thing. Can't quite figure out why there are so many fuse. The chassis is very 800'ish but the layout is odd. It was an open back bass combo with 4 horrible sounding 10" "marshall" speakers, cheesy plastic hand grips and castor wheels which i ended up stealing to use on a 1960a cabinet. I bought the 4150 for about $175 figuring, since it worked, it probably had good iron and i wouldn't feel bad tinkering with it since it wasn't prized vintage stuff. This is my favorite period for Rush though I had no idea what amps he played. I was really expecting something to be wrong with one side of the bias circuit. What really confused me was that they measured fine when i check the bias the first time and thought they shouldn't drift 'that' much. The amp still sounds way better than with the tubes that were in it before and the bias current seems to be stable now. I have their 6550's in my 2104 which I am very happy with. I will probably try Svetlana's next time. I purchased a few other things at the same time that seem to be fine. I bought them from antique electronic supply but am hesitent to sling smelly stuff at them because i can't say with certainty that my amp didn't damage them. I don't know how he used the 4140s, whether specifically just for clean or distorted tones, but effects included an MXR distortion, a MXR Microamp preamp, and Advanced Audio and Roland digital delays. See here: Quick glimpses of the rig are at 4:59-5:16, 7:03 Still, with the Howard Roberts fusion guitar, Alex's lead on that song is definitive prog! I would include Tom Sawyer in this list, but alas, it is so cliche' when mentioning Rush. Live versions of The Trees, Xanadu, Limelight, Jacob's Ladder, Red Barchetta, Freewill, and La Villa Strangiato were just bone-crushing using this setup. Many would argue that this was a great period sonically, if not the peak, for Alex's live and recorded sounds. Jaysg wrote:I will admit that I don't know much about those Club & Country models, however, they're from a decent enough era.Īn interesting note about the Club & Country: Alex Lifeson used a pair of 4140 combos with a pair of 100w Hiwatt heads and 4x12s for studio work and live for Rush's Exit Stage Left/Moving Pictures tour in 1981. I am not entirely sure pin 1 should be connected to pin 8 before going to ground through the cathode resistor but the metro amp 100w assembly manual showed it that way as a revision to the previous metroamp assembly manual and claimed it was more accurate this way. **I used a 1 ohm 1 watt resistor from ground to pins 1 and 8. Not too different than with the old tubes! I haven't had a chance to measure any resisters yet but none look burnt. I shut down right away.Ħ) I backed off on the bias trimmer a little, Voltages have not changed but now the bias current on the new tubes measures 25-26ma on the left side and 10ma and 15ma on the right. Plate voltage dropped by about 2 volts after the bias current was adjusted but was still virtually identical accross each tube.ĥ) After about 15-20 minutes playing on half to three-quarter volume in very low light, I see that the right two tubes are running too hot and starting a small glow spot on the plates in each right side tube. It sounded much nicer than with the old tubes, more detail. i'm pretty happy as it seems all the measurements are much more consistent and i believe in the right range.Ĥ) I did turn the bias current up to 28-29ma before pluggin in. after installing a matched set of EH tubes, I measured 24-25ma on all tubes. I haven't found much info on the 4150 but i have a schematic and it shows resistor values for el-34's are present in my bias circuit, not for 6550's.ģ) Cathode resistor bias measure** with the old tubes was 21ma, 25ma, 9ma and 13ma. Power tubes were a mismatch set of various brand el-34's (2 ruby's and 2 service master's which say made in w.germ). I wanted to would check the basics first, such as proper output tubes and biasing.Ģ) Measured 451v on all plates, -42v at bias pins. Thought it might be a decent candidate to change into a 1959 with a metro amp board kit and an additional preamp tube (the 4150 only has two) but haven't got that far yet. I've had it since the late 80's, and used it occasionaly but never found it very inspiring tonally. 1) I have a marshall 100w amp with el-34's.
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