Quote Originally Posted by kilohertz View Post
I noticed a little trash on the throat screens..perhaps a cleaning is in order .

I haven't pulled the xovers apart again but I am now wondering about different versions to accommodate the 16R 604. I have only seen one schematic published for the M/L xover and it isn't mentioned what the impedance is. I'll attach the drawing I have and a few pics of the driver.

I haven't ever taken one of these apart, is there anything to watch out for in dismantling the 604? Will I be able to get to the throat screen?

Thanks all, I hope I can get the highs back, after all, they were used as studio monitors for many years.
I talked to Bill at GPA about the screens on my 604s, and he said that you would have to remove the horn to get at the screen, this would be very difficult for you do yourself. I would have a go at cleaning them with a long cotton swab and some soapy water or isopropyl alcohol, and then some gentle sucking with a bit of flexible tubing hose inserted into a vacuum hose, so that you only get a fraction of the sucking power of the vacuum and you can throttle it with your hand.

If that doesnt fix your highs, put a multimeter on your 604s and check the resistance. Good to do that anyway.

My bet is maybe one of the parts in the xo is the culprit. Move the wipers on the attenuators back and forth several times to "clean" them. Or better yet, if you can get some deoxit or something on them that would be good. And then put the MM on the various parts of the xo to see if they are all in spec.

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from Altec Big Red Monitors - Page 2

I could say with the absolute confidence that bigger portion of that coil goes toward junction of 20 ohm resistor and 2.3 uF cap. Not vice versa as it was shown in this schematic posted above.

Corrected M_L_604_Xover.jpg