Gibson G20 Main Filter Cap Replacement Problem

[Perkinsman]

My friends G20 (at least I think it is since theres no model name on it) came to me not working so I looked inside and found what looks like corrosion around base of one of the 2 cans. Both cans say 2000mf/35v (semi circle icon) and Common Neg (triangle icon). I had a 2200/50 and removed the wires from each tab and reattached to the new cap. My first mistake was that I didn''t take a pic so I reattached based on my recollection since there were only 2 wires at each tab. I attached the 2 black wires to the negative side (Triangle) of the new cap and the 2 red wires to the positive side (semi circle). When I turned it on I had a strong hum so I shut it down immediately. I'm embarrassed to admit that I'm not very good at reading schematics and the one I found here when I searched Gibson G20 is confusing me. It shows one of the two filter caps C14 as 150mf and C15, the other value is not shown but the parts list says 2000uf.

So....one problem is I'm not sure which one I'm replacing since both cans actually say 2000uf. Secondly, even with the new 2000uf cap installed why do I have a hum? When I happened to detach one of the black wires, the hum stopped but the amp doesn't make sound. Did I attach the wires incorrectly?

Can someone please help me sus this problem out.

[drewl]

The amp is using only positive voltage for the power supply.
the cap you installed looks like it's backwards as the negative side should be grounded.

[Perkinsman]

Ok, I’ll try that but is it the cap 150 or 2000uf?

[drewl]

2000uf, like you have.
2200uf the more common current value.

[Perkinsman]

So is the other can the 150uf because it says 2000uf on the can?

...and does the detached black wire go to the negative side as well?

[Enzo]

The amp used to work at some point, and it had a pair of 2000uf caps. Why would we want to change the value now? 2000uf are in there, so replace them with 2000uf.

[Perkinsman]

Ok, I‘m just learning & thought following the schematic was the correct way.
Also, the IC was loose from the socket. Which way does it go back in? I don’t see a mark on the socket, only the IC.

[The Dude]

There are pin numbers on the socket at each end if you look closely.

[Perkinsman]

Thanks, I needed a magnifier to see that buts it’s in.

Back to the new filter cap install...I turned the cap around & soldered the 2 black wires to the negative side & the red&orange wires to the positive side. It still hummed. I then found one other wire that is connected to the rear foot pedal socket and grounds to the chassis. I attached that wire to the negative side of the cap & the hum stopped. However, the current meter on the variac goes up to almost 2.5A when I bring the main up to 120 & the new cap gets hot.

[The Dude]

You may have damaged the new cap having installed it backwards.

[Perkinsman]

It’s not the cap, I’ve tried several others, same result. Does my wiring to the cap seem correct?

[Perkinsman]

I was incorrect about the hum going away with the white wire connected. The speaker had disconnected at the other end.........it’s back on the speaker again now & the hum was still prevalent

[drewl]

Do you know if the other can cap is good?
can you sub in another?

You have any way of measuring voltage or ripple?

[Perkinsman]

I’m pretty sure the other cap is good but I can sub it out if needed, however there wasn’t hum until I changed this cap out so I’m sure that the hum is due to my wiring incorrectly. That’s why I needed a pair of eyes to check it out. Yes, I have a DMM.

[The Dude]

Well, you have the schematic. The negative side of the cap goes to ground. The positive side goes to the output of the bridge rectifier. Verify your connections with a meter