![]() The PT primary blue tap is tied to bottom terms of polarity where the yellow hot from fuse/black power cord hot is also tied and PT primary brown tap is tied to the 120VAC tap of the multi tap AC power board and is tied to the bottom terms of the power switch by a black wire to the 120 tap connection board. As shown in the picture the power cord white is tied directly to the polarity two top terms, the hot through the fuse comes by the yellow wire to the polarity switch two bottom terms and of course the two middle terms go through the cap to ground. I have been reading previous post and looking at the situation. That way it would still be holding it's original part in place couldn't get lost being there bolted in. On the three conductor cord hookup my plan was to leave the polarity switch in place but more or less disabled. OK, I'm proceeding on with first the three conductor cord and then the MV. It would be good to know if its not original. Maybe I need to check the numbers out more closely on the PT and see what I can find. ![]() You want to see if the heater voltage is high too huh? Well if somehow the PT is hooked up wrong, I sure would like to know myself. I've got to take it down again and probably do a three conductor cord and maybe a MV mod, so I will do it then. Jim-You know when I had it opened up the other day, i forgot to check the heater voltage. ![]() So sometimes you get crazy ideas in your head. I bought a Peavey Mace because in those days I was a big Skynyrd fan, it smoked and I had to send it back to the factory under warranty for a new board. To top that off when I was living in Oklahoma City in 1979 I seen first hand Marshalls break downs on stage and the techs were going crazy trying to get it going again. Back in the 70's when I was doing a lot of playing/traveling I always heard reports that they were UN-reliable. So both channels are clean? OK! I take it you were not to happy with your JMP 50?įor some reason, I don't know why, I've always resisted Marshalls. I just plugged into channel 2 briefly and could swore it had more gain than channel 1 but I turned it up louder also. 7 = 37.8 mA bias-BTW that's pretty close to Webers calculation If I did this method/calculation correct, looks like the bias is way cold!įor Even more added Pleasure: E元4=25 watts divided by 464 Plate voltage =. I'm not Marshall knowledgeable but they seem pretty OK, to me.Īlso for added fun-I tried VMS's method he pointed out in post #40 for measuring resistance across the two OT primary sides, then measuring the voltage drop and dividing the voltage drop by the resistance-if I understood it right? here goes: For those why know what the voltages should run on this amp, please check it out and let me know if they are OK. According to the Weber bias calculator running AB with E元4's at 464V plate voltage bias should be 37.7 mA. So I need to get down to what the bias mA should be running that plate voltage. It's pretty high on the power tube side(464), but that may be right for this one-you tell me? No red plating detected and the tubes don't feel abnormally hot. Boy is this thing loud!!!!Īnyway I'm not familiar with what Marshal voltages are suppose to be since they didn't put the expected voltages on the schematic like fender. So I pulled out each preamp tube and tried a known good tube and when I got to V1 it started working fine. Had a rough time at first because I had no sound with a guitar plugged in but could hear the amp driving the speaker. Voltages are provided/recorded on a scan of that 1987 schematic attached below. I just got through firing it up for the first time. Well it won't be the first thing I put together I didn't understand but still worked
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