Ampeg B22X with multiple problems

[Randall]

The jack is making a good connection. My question was actually whether or not being grounded at the chassis could be an issue since the proper switching jack is isolated.

[DrGonz78]

Well I thought I misunderstood what you wrote when I typed that part. In the schematic all of negative side speakers terminals tie together through to chassis ground. I guess there is a difference from the way the schematic presents the connection compared to the layout. To answer the question then I would remove that jack and solder a wire to the ground connection right at the OT, floating the jack from it’s original chassis connection. Not sure it will make a difference but if it does then there you go.

[DrGonz78]

Also I see how they actually have the two speakers running in series. So my last statement that negative speaker terminals run to ground was not true. But still the one that leads to negative is chassis ground.

[Randall]

I have checked grounds, lifted my temporary speaker jack wired to the 8 ohm tap from chassis ground, and wired it to the ground lug the real isolated speaker switching jack is grounded to, and clipped in a 22uF/500v cap to all six filter caps, and none of it made any difference. I scoped the sections of the can cap as well as the two 30uF/600v, and while I see a little fluctuation when the machine gun happens, it isn't much, and I amd not letting it bang on my poor speaker long enough to get a real measurement.

One bit of progress is the dead channel 1 is now passing signal after I returned V8 back to it's socket. One thing that still vexes me is that the can is not chassis grounded anywhere that I can see, yet it measures as though it is.

Where to go from here? Help!

[DrGonz78]

Can you post a picture of the can cap and it’s wiring?

[Randall]

The black wire at 12:00 is the two 30uF/600v cap grounds. The black wire at 3:00 is OT ground. The three black wires at 9:00 are speaker jack, output tube cathodes, PT center tap to standby switch, and main board ground. Please excuse the red and orange wire connections, I had disconnected them to measure the can sections, and only tacked them in for now.

[g1]

Did the original cap can shell connect to chassis? Does this one?

[DrGonz78]

So it’s makes chassis ground through the standby switch. So when the amp is off check resistance right at the cap can lug while toggling the standby switch. Does that confirm that the standby is the only connection to chassis?

[Randall]

The original cap can shell did not make connection to the chassis, nor does the new one. I made a map prior to disconnecting, and followed it exactly.

Gonzo, I do not see your argument that the standby switch is connected to chassis. One side is PT CT, the other goes to cathodes, isolated speaker ground, main board ground, and 9:00 lug on can. No chassis ground that I see.

[DrGonz78]

Look on the schematic at the standby switch. When the switch is in standby it floats the ground connection. I am just going by what the schematic shows. The other connection to ground would be the input jack. All of those can lugs are at the same potential since it is the outer can connections. You did say the outer can is connected to chassis but cannot say why.

[DrGonz78]

One thing that still vexes me is that the can is not chassis grounded anywhere that I can see, yet it measures as though it is.

This is what I was referring to.

[DrGonz78]

Also on the schematic it shows cathodes of the power tubes going to chassis ground.

[Randall]

Gonz, I'm not really sure what point you are shooting for. We have established that all grounds go to the cap can lugs, with the exception of the input jacks, but the can itself is not bonded to chassis. It seems an unusual grounding scheme to me, and it must be connected to chassis elsewhere that I do not see, based on my measurements, but are we really on the right path at this point? I need to figure out this loud hammering sound before I lose my shop speaker.

[Randall]

Concerning the current state of affairs I find myself in with this amp, not being able to figure out why it is hammering the way it is, would anyone think it worth replacing the can cap and two 30/300v filter caps? Also, I would add the OT is a new replacement from Fliptops, is there any possibility it could be the problem?

[Randall]

Help! I'm really stuck here.