Metropoulos Forum

Alrighty Metroampers... I have a doozy for you guys. No one seems to have any answers on this one. Maybe someone can offer a jem.

I'm rebuilding a 100W Super Bass clone and so far very few hiccups, things were looking really good. However, I've ran into a problem that no one seems to be able to help me with which is why I'm resorting to an emergency post!

I get proper voltage readings in my amp and everything appears to check out great. When I take the amp off standby it makes that nice slight hiss when I crank it all the way but besides that no ticks, noises or anything else to speak of.

When I plug into any of the input jacks everything goes good and no noises or bad sounds. I can turn up the amp volume all the way with my guitar plugged in, still no noise. I can also play single notes or some very simple two note chords and still no noise. However, whenever I turn up my guitar all the way, or play a full open chord I get this terrible diesel truck noise through the speakers. The noise starts medium/low pitch and then gets lower and lower. After about 15-20 second the noise stops. It's quiet again until I try to strum a chord again. Then the same thing happens. I've tried moving wires and checking the ground to see if it's some sort of ground issue and nothing seems to make a difference. Unplugging or turning the volumes all the way down makes no difference once the noise has started.

No answers so far... Any info at all would be very greatly appreciated.

If you go thru the amp, starting at v1a, and touch your meter probe to the grid on the tube socket directly (dont crank the vol way up), do you get a pop noise in the speaks (you should if all OK)? This can eliminate per section any wiring/connectivity issues.

Possibly a bad ground or a cold solder joint somewhere is giving you an intermittent and/or poor signal path.

Have you subbed any tubes yet?

Dave

Thanks for the reply Dave. I have swapped all the tubes, and no change. I'll definitely go through the amp and check the grids as you suggested. I don't really have a reason for this, but I have a sneaking suspicion that it's a ground problem... Anyways I'll post back when I get it done an hopefully we can knock one more thing off the list.