Airline GIM-9131A knowledge/repair question

[btah]

Put in the new cord. Not much of a difference. The Dude indicated I should get rid of a capacitor. There is no capacitor that was attached to the lug the power was attached to. One of the power wires attaches to the reset switch, the other to a bank of connections. The individual connection the wire was attached to does not have a capacitor attached to it. There is a capacitor on the connector next to where the power wire was connected, but there is no type of connection between those two locations.

I will provide more information tomorrow on full functionality of the amp and what is still an issue.

[The Dude]

The cap is on the center of the line reverse switch, which ties to either side of the ac in depending on switch position. See the schematic.

[btah]

So that cap doesn't exist on the amp. In fact, I think something funky is going on with the line reverse. The pictures shows the line reverse switch. The wire coming from the left is a power wire coming from where one of the wires from the AC cord hooks up. The wire going off to the right leads to the panel light switch. Nothing else. I can see on two other lugs of the line reverse switch there was once solder. I have no idea what the line reverse switch is supposed to do but I think it has something to do with the AC coming in. Could this explain why we had to originally switch the wires on the output tubes?

[The Dude]

Someone has apparently removed the cap and bypassed the switch. Already taken care of. We can move on from the death cap. This would have nothing to do with the OT wires.

[btah]

What is the real purpose of the line reverse switch? Wouldn't it be important to someone playing or is it strictly an electrical thing because the amp wasn't grounded?

[btah]

On to the next thing that is bugging me. Again, this I am sure is going to be just a lack of knowledge thing, but it doesn't make logical sense to me. See the picture. There is a coax cable that goes from v1b grid to a bank of connections. Here is what makes no sense to me. The coax has the wire in side the shield and then the copper wire that is wrapped around the shield (the ground, right?). Hooked up to the v1b grid is the wire inside the shield. That hooks up on the right side of the amp on the left connection. The copper wire in the coax hooks up to the right of that, however, the side of the wire at the tube hooks up nowhere. It makes no logical sense to me that the copper wire would be hooked up on one end but not on the other. The same setup is used for the v2b grid connection. What the heck, why does a wire go nowhere? Or did I just show how little I know about electronics?

[The Dude]

The line reverse switch, when it was as new, would "ground" (via the death cap) either side of the AC line coming in and was switchable to either side. Irrelevant now that you have a 3 prong AC cable.

As to the wire you show in the picture, I'm not completely sure from your description what you mean and we can't see the other end of the wire. I'm assuming you mean that the shield is only hooked up at one end? This is not uncommon as it is just that- a shield to keep noise out. It need only be grounded at one end. I will also add that RG59U is television coax cable. It's unlikely they would have built the amp with that stuff. Someone has fiddled with this amp in the past.

[btah]

Well, I was working on a another reply and had a bunch of information typed in and wasn't paying attention and got logged off. I don't have it in me right now to redo it so I will pick it up tomorrow. But you assumption as to how the wire is hooked up was correct. The remaining issues, i think, are buzz and the reverb.

[52 Bill]

As to the wire you show in the picture, I'm not completely sure from your description what you mean and we can't see the other end of the wire. I'm assuming you mean that the shield is only hooked up at one end? This is not uncommon as it is just that- a shield to keep noise out. It need only be grounded at one end. I will also add that RG59U is television coax cable. It's unlikely they would have built the amp with that stuff. Someone has fiddled with this amp in the past.

Agreed, the shield is only connected to ground on one side to prevent ground loops from forming.

[btah]

The buzz: Two different types of buzz going on.

Deep buzz
channel 1: WITHOUT a guitar jacked in there is a very deep (I am going to say the lower end of the bass scale) buzz that gets louder when the volume is turned up. No deep buzz when the volume is off. However, when I jack a guitar in, the deep buzz goes away. Also, if I put the jack into the amp input and remove the other side jack from the guitar, the deep buzz gets louder than if there is no jack at all in the amp.

channel 2: no deep buzz whether there is a guitar jacked in or not.

not loud buzz, not nearly as deep as above
the buzz doesn't seem to be tied to either channel one or channel 2. IF I have the guitar jacked into channel 1 so the loud/deep buzz goes away, the not so loud and not deep buzz is consistent and the volume control of channel 1 and channel 2 DO NOT make the buzz change. Also, this buzz has a rhythm to it. It seems to be pulsing maybe 3 or 4 times a second.

[The Dude]

The input jacks should be switching jacks. The tip should be shorted to ground via the jack when no guitar is plugged in. It sounds like either A) the switching jack is not working, or B) the jack has been changed to a non-switching type. So, how many solder tabs are on the jack itself? Also, it is normal for an amp to hum when only a guitar cord is plugged in with no guitar attached at the other end.

[btah]

Hooked up to the input jack is only a resistor. All the input jacks are set up the same way.

[The Dude]

The picture answers my question. There are only two solder lugs on the jack. A switching jack would have 3. That is why it hums. With no input, the tip of the jack is ungrounded and "hanging in air". You need to replace the input jacks with this type. (note 3 solder lugs and the switched tip connection)

[btah]

So I can eliminate the jack by simply unhooking the resistor from one of the ends, correct? Then I know the jack is the issue.

[The Dude]

NO. That is the problem. when nothing is plugged in, the jack IS already unhooked and not grounded. If you doubt me, you can ground the jack to prove that it is the problem. The correct jacks, would ground the tip when nothing is inserted. They need to be replaced with the proper jacks- all inputs.