Hello guys . I am one step to finish and test the clone of Marshall jcm 800 . I’m waiting the power and output transformer and also the choke .. check my progress … on the last photo see the red and black banana terminal and also the switch and the hole with trimpot inside , this is the bias setting . I make it for fast setting the bias without put out the chassis .. just put the multimeter on terminals and push the switch on right side shows the high volts of plate ( EL34) and on the left side shows the mV .. and adjust from trimpot 😀
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Guys ! Someone help me .. problem with biasing .. let’s start what I’m doing : connect 1ohm resistor from 8-1 pin both of el34 to the ground … I leave on standby the amp with the speaker connecting and the pots on zero … after 30 minutes I turn on the standby ,,,checking the pin 3 ( el34 plate ) and I wrote down 479 vdc ( I see the same with other el34 ) .. now I’m using this formula : 25/ plate voltage * 65% …for me is 0.0339 = 33-34 mV…. So I’m going and check the pin 1-8 and start to dial the trimpot ,, after 7-9 mV the speaker start makes a loud noise like (eeeeeeeeeeeeeee) …the one problem is that the other problem is , the mV of pin 1-8 of one el34 it doesn’t the same with the mV of pin 1-8 on other el34 , like on first el34 is 6.5mV and on other is 2.4 mV , something like that .. and the el34 are matched ….where is the f&@ing problem !?!?! Thank you
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