another coliseum lead question

[cromag]

so i bought a coliseum lead and two sunn 4x12 cabs for 500 bucks a few weeks ago.  i cleaned the head inside and out and sprayed some pot cleaner on all the pots etc...    the second input on the top channel is real quiet.  no biggy as the first input works and sounds fine.  the problem is, when i turn this head on or off it makes a loud pop.  even with the volum turned all the way down.  when i was turning it off last practice, i did it slowly and the pop seemed to act directly with the actual "click" of the button.  in other words, if i just turn it on / off quickly, the pop is real quick.  when i turned if off slowly, the pop kinda snapped then popped a little more accordingly with the switch moving all the way to rest.  any idea what causes this and how could i fix it?  thanks all.

[CLD]

As I understand it (and recall ... vaguely), it's a pretty common characteristic of 1970s solid-state gear.  Both my '73 Coliseum Bass and '74 Coliseum 880 do this, though my '72 Concert Bass doesn't.  I've been told that's just how they are and that there's no fix.  However, there are plenty of smart people who post on this site so someone may know of some remedy.  Although there's still a loud "whuuump" when turning the amps on, I always keep the volume at 0 just for good measure.

[cromag]

cld,  i agree with the volume being turned all the way down when switching on / off.  i am just concerned about the speakers being overloaded with that loud pop when turning on for the first time.   however, since posting the first question, i have turned the amp off very very slowly controlling it's movement with my fingers and was able to shut it off with not much of a pp at all.  so, maybe slow is the way to go.

[CLD]

I worry about the speakers, too.  To correct my earlier post, the Concert Bass has a much quieter whuuump, but enough of one to hear it when turning the thing on.  Good tip on turning it off. Thanks!