Audio Research Classic 60 & 120 owners


For those who own one of those, does the power transformer (left one on the 120 and the center one on the 60) get quite warm to the touch after a few hours of operation? Mine get very warm. So much so that i can hardly keep my hand on it for very long. The bias setting is dead on with SED 6550C. Mine were upgraded by GNSC back in 2004.

This is not a new phenomenon. They have been warm like this for as long as i can remember. I had meant to ask other owners but never got to it until today.
Any feedback much appreciated.
smoffatt

Showing 7 responses by hifigeek1

I have worked on quite a few CL-30 and CL-60. Yes the transformer does get quite warm. I also remember the power transformer being close to the output tubes. They are designed to run at that temperature and if there was an issue with too much current being drawn through the transformer your line fuse would fail provided the fuse is the proper current rating. You might want to consider replacing your filter caps at some point. I've had to replace those too.
My guess is you have a faulty tube or tube socket. A lot of times a tech will miss either corrosion, if you happen to live near the coast, corrosion can occur under a tube socket, or you have some corrosion on the circuit board. It is also possible that you just have a bad tube socket, it's loosing it's dielectric strength and arcing to an adjacent pin. I have a D115mkII I'm working on right now with a similar issue. BTW it's not a rectifier issue as rectifiers do not become intermittent. They either work or they don't. Question, when you look at the blown fuse, is it hard to tell the fuse blew or is the metallic fuse element splattered all over the inside of the glass tube? That unit I believe uses a servo to match the bias from a pair of output tubes you set the bias on. It's possible and not at all unusual for the servo to not 'pull in' properly and so the servo'ed side of the output tubes are running away. I will look at a circuit diagram to confirm that but I believe that whole series, CL-30, CL-60, CL-120 used this servo bias arrangement.
There is also a way to 'speed up' the servo so it pulls in sooner but that is something a qualified tech should do with parts and documentation from ARC.
Yes, the fans must be on in order to properly cool the tubes and the surrounding components.