Does anyone have any suggestions regarding what solvent to use to clear away the tar in the crossover? It still smells fresh after 47 years, but it covers nearly everything, making it impossible to really see what's inside.
My N-800-G crossover has stopped sending any high-frequency signal. The high-pass leads show as open on my multimeter. The 806a driver works OK and lows pass to the 416a woofer with no problem. The pot is also OK and is perfectly clean. The crossover has never been opened before. I just opened the crossover to find everything encased in shiny, black tar, so it's a bit hard to locate anything. Any suggestions as to what, specifically, may be at fault? Anybody have a schematic for the N-800-G?
Does anyone have any suggestions regarding what solvent to use to clear away the tar in the crossover? It still smells fresh after 47 years, but it covers nearly everything, making it impossible to really see what's inside.
A lot of the vintage Altec crossovers have that tar-like substance inside the crossover. I've owned several. If I recall correctly, the best way to remove it is to warm the crossover up in an oven at 200 degrees for 15-20 minutes (and no more than that) and that will make the "tar" soft enough to remove. There are members here who've actually done this with success--perhaps one of them will chime in as well. That's the best way to soften the "tar" as far as I know....
Being of "Sound" Mind
Never tried the stove, just a commercial 1 kW heat gun that requires a 20 amp outlet. Anyway, these XOs are way past old enough to need their caps replaced and I assume one has blown.
GM
edit: Maybe this cheap heater or similar will work without resorting to smelling up the oven: Heat Gun - Dual Temperature Heat Gun, 1500W
Last edited by GM; July 22nd, 2013 at 03:31 PM.
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
If you do go through the effort to excavate the XO from the tar pit, please post pics - I'd love to draw a schematic and get it posted up.
- Mike
Thanks guys. Heating slightly made the tar peel away easily, revealing 2 chokes and what I assume is a box of ELPAC capacitors. Here are some preliminary pictures. 001.jpg
Last edited by kimchi2; September 3rd, 2013 at 02:02 PM.
Replacing the 4mF cap in my Altec N 800 G dividing network which wasn't passing the high-freq signal solved the problem completely. The original ELPAC capacitors are in a small, wax-covered paper box labeled ?10.5 mF" and "4.0 mF?, exactly as you'd expect. Curiously, when I removed the caps from the box, I found that the big cap is actually labeled ?10.0 mF?, not 10.5 mF as indicated on the box as well as in other XO documentation I have seen. I have replacement 10 mF and .5 mF caps so I can choose either value. Should I choose 10 or 10.5 mF for the replacement? Which value is truly correct? The crossover is connected to a 416a woofer and 806a/811b in a Valencia-style cabinet. Pictures of the innards follow.P1010321.jpg
Either 10 or 10.5 is likely "close enough"
Bear in mind devices have variances. Unless you check them, a 10.5 labeled cap might be really a 9.5 and still leave the factory labeled "passed QC".
This is audio, after all, not space flight.
Your neighbors called. They like your music.
Thanks, Old Guy. You are right: I get a bit too obsessive about minor details. BTW, I just tried it both ways and both sound superb.
Figure a good cap is 105 tolerance, 10.5 could really be 9.45...or 11.55
If you have a capacitor checker you can order half size caps, test, then match up paralleled pairs. But a lot of work for minimal gain.
Your neighbors called. They like your music.
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