Gibson G20 Main Filter Cap Replacement Problem

[Perkinsman]

Ok, thanks Dude, I removed that wire to the jack ground and put them on the same ground lug. Then I followed DrGonzo's DLab picture to which I am also indebted because now the amp works again. It still hums a little, definitely alot less & it used to squeal too so that's totally resolved. I decided to also replace the 2nd filter cap and a few of the caps on the board and touched up alot of the solder joints. That still didn't eliminate the slight hum so I'm going to replace the older 2 wire power cord. Should I ground that to a ground lug as well?

[DrGonz78]

Take a picture of the two prong wiring so we can see if it has the notorious death cap nearby. Strange that G50 schematic shows a grounded three prong power cable.

[Dave H]

I'm going to replace the older 2 wire power cord. Should I ground that to a ground lug as well?

No, the "safety earth" should be bolted directly to chassis with its own bolt.

[J M Fahey]

Iīm baffled that you canīt read schematics yet take amps in for servicing.

[DrGonz78]

I suggest that you build an amp from the ground lug up. I could already read a schematic when I built a little champ amp but after that build it improved my schematic reading even more.

[Perkinsman]

I really want to do that! Do the kits teach you how to follow the AC & DC paths through the amp. That's where I get mixed up, I'm not sure of the direction of the voltage so I'm not sure what points in the path are important to test and how to calculate what the approximate voltage at those points should be. That would be helpful with troubleshooting which is a challenge but just the symptom, the underlying cause is my poor schematic skills.

About the ground power wire to it's own lug.....I'll be doing that but doesn't "chassis ground" on the schematic imply any ground in the entire circuit is physically attached to the chassis & that they all share the same ground point?

[Perkinsman]

Iīm baffled that you canīt read schematics yet take amps in for servicing.

True dat, I can read most of them but I don't know how to interpret them well yet...but I'm also a decent musician and I don't read music well either.

[DrGonz78]

I really want to do that! Do the kits teach you how to follow the AC & DC paths through the amp. That's where I get mixed up, I'm not sure of the direction of the voltage so I'm not sure what points in the path are important to test and how to calculate what the approximate voltage at those points should be. That would be helpful with troubleshooting which is a challenge but just the symptom, the underlying cause is my poor schematic skills.

About the ground power wire to it's own lug.....I'll be doing that but doesn't "chassis ground" on the schematic imply any ground in the entire circuit is physically attached to the chassis & that they all share the same ground point?

The kits don’t teach you anything other than it forces you to follow the road map. It makes you start comparing the schematic to layout in a way that you will start to figure more things out with specific questions that arise. Once you learn signal flow in one amp schematic you will start to see it in others. It’s that AHA moment when you start really seeing it natively. Look up Rob Robinette’s website and analyze signal flow through a tube amp. Start there and then later focus on signal flow through solid state amps too. Force yourself to absorb a little each day and eventually you will start reading a schematic in depth.

[g1]

Look up Rob Robinette’s website and analyze signal flow through a tube amp. Start there and then later focus on signal flow through solid state amps too. Force yourself to absorb a little each day and eventually you will start reading a schematic in depth.

Lots of good stuff on Rob's site, here's a link to his 'reading schematics' info:
https://robrobinette.com/Reading_Tub...Schematics.htm

Also highly recommend the Jack Darr book, (not sure if this is complete book):
http://www.trinityamps.com/ForumGall...r_Handbook.pdf