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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Re: Help with dysfunctional MC 240 posted by Steve O on March 27, 2007 at 11:04:23:
I agree with Steve but want to add a couple of comments: The higher signal level stage voltages you're experiencing are probably the result of the output tubes not drawing current thus there is less voltage drop from the power supply - they should stabilize once the output stage is back in shape. You might have a heater/cathode short in one of the outputs which would wobble your heater voltages - especially since one side of the heater circuit is grounded. As to the control grid you've got the bias rectifier and bias filter - which being electrolytic caps probably need replacement if this hasn't been done. Mac circuits are a bit different but there is a 0.47uf cathode
"bypass" cap for the each output tube that connects to the split cathode resistor on each of the 12AX7 drivers which may produce some of your control grid symptoms if leaky.If you can do the job I suggest that you do a filter recap job on the amp - mosty amps of this vintage could use it - and replace the output tubes cuz I wouldn't trust the ones that have arced. And it wouldn't hurt to replace C9,10,19 & 20. Otherwise follow Steve's advice and take to a reputable shop.
Rob
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- Re: Help with dysfunctional MC 240 - Rob Mercure 15:12:20 03/27/07 (0)
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