Sunn Concert Bass sounds bad at volume 5 & up

[stevef]

I have a concert bass head, 150 watts RMS that sounds pretty good with a pbass if I crank the bass and keep the treble low on the amp. This works up to about volume 4. After that the amp just loses it and sounds honky, middy and does not project any clear low end. Is this a sign that something needs to be replaced? It is  a 1973 head and I just use it for practice but would like to turn it up for a show too. Thanks in advance.
Steve

[Anonymous]

I have an old Concert Bass too.  It kept cutting out, sounding weak distorted, whatever.  I feared I might be losing an output transistor, but when I opened it up I saw the problem: The circuit boards and components are connected by connectors that just slide over corresponding metal posts.  Over the years (and with the vibration of bass frequencies)these connections became loose and corroded.  To fix, I soldered all of the connections--yep, all of them--and the amp worked great.  You may need to spray the connections with a good cleaner from an electronics store before you solder them.  Also: the main circuit board mounts on cheesy little plastic standoffs, these become brittle and break, letting the main board move around--potential for short circuit.  I made new standoffs from a plastic ink pen and screwed the board down.  Oh, and get a can of Deoxit and lube the potentiometers for the tone and volume controls.

[Rocketboy]

Don't spray the connectors with anything if you're going to solder them.  Clean them thoroughly first.  Also, as a matter of course, replace the filter capacitors (and all other electrolytics) every ten (10) years.  That will bring the amp back to new life.