BGW Legacy Amp Service Note
Another*SERVICE NOTE* for older BGW amps revolves around the use of MOLEX multi-pin connectors to attach the power modules to the amp's wiring harness. (The larger BGW amps use octal plugs / sockets and are subject to the same time mediated malady.)
I have a large group of BGW 150 (1 RU height) amps that I use to drive JBL 2404 "Baby Cheek" tweeters. They would intermittently hiss, pop, and fart... I looked at the amps' output on the oscilloscope with an 8 ohm dummy load driven by a 1 KHz sine wave. I drove the amp at 75% rated power. With the cover off the amp, I poked around looking for noise sources -- I used freeze-it spray to see if any active component had 'gone thermal." NO DICE!
Remembering some tube type troubleshooting, I tapped the output modules and saw some noise spikes on the oscilloscope. I thought maybe the thermal paste on the power devices a degraded, so I spent two hours removing and renewing the thermal transfer paste. Powered up the amp, and the noise trace was still there. Out of frustration I tapped the 16 position MOLEX connector with a 1/2" diameter wooden dowel. BINGO -- the noise trace changed in direct relation to the tapping.
After power down, I used two pairs of slip-joint pliers to *GENTLY* separate the male and female connectors from each other. I examined the connectors and found them to be nickel plated -- and dull and grungy. I then sparingly used (one drop per receptacle / pin) some MARVEL MYSTERY OIL on both the female socket receptacles and male pins. I made and broke the connections four times and then powered up and tested the amp as above. Result -- no noise traces at all when when the MOLEX connectors were tapped. The amps sound clean, crisp and noise free.
Lesson -- look at the condition of the removable connectors first when tracing down intermittent amplifier noises.
Contact cleanup tips & tricks
On low-voltage contact points, oxidation can produce a "diode effect" that can make for a nasty sound quality due to the fact that the oxidized surface is resistant to current flow below a certain voltage level.
My personal favorites for contact clean-up and treatment is:
For power path:
Cramolin red liquid
CorrosionX spray
For signal path:
Caig DeOxIt spray (red or gold) (contains Cramolin)
Cramolin Red liquid
Caig MCL (blue) spray for sliders.
Use pipe cleaners on female XLR connectors etc.
Twist two or more pipe cleaners together for larger jacks.
Q-tips are generally useful on male connectors. Watch for any cotton fiber lint left hanging around.
Use toothpicks for stubborn spots and to remove lint etc.
Scotch-Brite cloths can be helpful too but take care not to remove the surface plating, especially silver or gold plating. Note: silver oxide IS conductive, and gold doesn't oxidize, so concentrate on dirt removal more than polishing the silver on these connectors. Use the non-abrasive blue pads if you can find them.
Gun cleaning brushes are especially useful, and are made with nylon or bronze bristles in a wide variety of diameters from .17", .22", and many other "calibers" up to .45" & .50"
Most are made to thread onto gun cleaning rods ( pistol rods are shorter & handiest)
Some cleaning tools are made like miniature screwdrivers with tips of different sizes & shapes.