Originally wasn’t like that, but I’ve was advised to do it! I have installed new ceramic 1K/5W resistors over pin 4 and 6, also aded 5.6K Grid resistor to grid 1! I have replaced the tube sockets with Benton’s! Thanks for Your Help again Lake Placid Blues, and Kind Regards! What value should be that cap, and with what is directly connected? I’am not so shure which one is it, but I am sure I have not replaced caps on the phase inventor circuit! I could start with that sucker: The coupling cap on the phase investor circuit! I could eliminate them one by one, and with better luck and instinct, that could happen in the beginning of the row! Looking at the schematics there couldn’t be so much possible issues that would affect the load of each power tube! That is definitely not the best scientific approach, but according to the circumstances, it could come practical! I don’t have special tools, but I can replace components! So now I have decided to learn more, and find my way out from that problem! Since I was studying around in the last six months and learned this and that, I found the bias he was setting was way too cold!Īssuming he didn’t consider my amp plate voltage is not 600V, but 400V! One is beyond my price range, the other was the guy who was retuning and biasing my amp in the last 10-15 years! I have replaced the original OT with brand new “Classic Tone” OT!īut don’t regret it! I am looking at the bright side! I have considered that possibility only by starring at the schematics and using my best available special tools! We have to write off the possibility of faulty OT! I have asked for help in various net forums, and You Are the first with specific suggestions! Re: Marshall jmp-50 2204 issue Please Help :-( yuck !Īny suggestions would be highly appreciated! I have Marshall JMP, and now i’am recording with amp simulators. No hum or any other signs of something being wrong?! What possibly can cause such a dissbalance Between the two tubes when amp is pushed!? I would guess, there is crossover distortion caused by the big difference in the current draw between V4 and V5! If I swap the tubes, the higher readings are still on V5! The lauder the amp is pushed, the bigger the voltage reading differences between V4 and V5 ! If I stop playing, both will go back to 37.0 37.4! The highest readings on louder lower notes on V4 was reaching 45mV, while V5 was going way higher to 130mV! , I found V5 voltage was jumping a lot higher then V4!Īnd as I said above,the more I was pushing the amp, the bigger that difference became! When I was swapping the probe back and forth between V4 and V5 The readings on the meter went up, which it should! I have one of these socket probes that goes between tube and amp socket with probes to be plugged in meter! I am biasing the amp, on mV setting on the digital multimeter!Īfter about 15 min waiting for the bias settling in ,I left the probe and the meter on the way it was, and start playing!
There was around 0.3~0.4mA difference between V4 and V5 at idle! Most JMP’s are on 600V, but few run at lower : at 400V! I was checking and rechecking the bias from time to time on a new purchased installed well matched pair of Svetlanas, and the last time I did it, I left the probe and meter on V5, and found something that definitely didn’t look right to me!?īefore that :My amp plate voltage is 400V! Well.with Marshall tube amps is supposed to be the other way around isn’t it :-)!Īnd I have tried it with all different preamp and power tubes! On low volumes it is not that bad, but the more I push the preamp when master is more then 50% (5-6), the worse it sounds! Tubes, filter caps, trim pot,bias caps, pots, jacks tube sockets, a lot of other caps! I have replaced everything I could think of and I could! My name is Steve, and I have JMP-50 2204 amp with E元4’s!
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