Image of a Marshall 1960B Jack Plate

[TremoJem]

I have disconnected my 1960B jack plate (JMP53A, 1960 Stereo Jack Socket PCB) and did not make note of connections for re-connecting them.

I pulled the back off to check each speaker when isolated (each read 12.9 ohms) to make sure they were all good.

I went to reassemble the jack plate and did not know where to put the damn connectors.

After I get this assembled I intend to make a test cable and insert it into each jack in an attempt to check impedance of each jack and it's associated impedance rating according to what the selection of the stereo/mono switch.

I figured if each speaker is good to the pcb and then my readings are good on the other side of the pcb then all is good and I can use it without risk to my amps.

If anyone has a pic or really knows where the four wires go on the jack plate it would be a big help.

All I really need is polarity as each side is the same as the other. I keep the right to the right and the left to the left but when going to connect to the pcb I can't remember polarity.

One last thing, after I re-connect and check this out and determine that I want to use it, is there a REAL advantage to upgrading the wire from the thin maybe 20ga wire to thick 16 or 14 ga wire and soldering the connections instead of using the slip on terminals?

I have already tightened all the hardware and have insulation upgrade ready to install. I could not believe how loose the speaker hardware was.

Please help.

 

[TremoJem]

Found it...

http://www.mojotone.com/amp-parts/am...Plate-Double-1

 

[94Tremoverb]

The best thing to do with this jack plate is first to take off the PCB assembly and throw it as far away as possible. (OK, maybe keep it somewhere safe... just in case you sell the cab.) Then get two standard panel-mount jacks, fit them in the two holes, and wire them in parallel and connect them to the speakers - wired for either 4 or 16 ohms, depending on which you need - with all-soldered connections.

These switching plates are unreliable and can blow your amp's tubes or output transformer. They look like a useful thing to have, but consider that the speaker current has to pass through four switch contacts in the slide switch, four jack switch contacts, and four push terminals, plus multiple PCB solder joints and the PCB traces. If *any one* of these fails in the 16-ohm mode, you've got an open circuit. If certain ones fail in the 4-ohm mode the same thing happens. The jack switch contacts in particular are prone to problems, especially if the cables have been tugged a few times and the contacts get a bit stressed.

Just a bad design - making things much less reliable than they need to be for very little practical purpose. I've seen more than one amp with a blown output transformer that I'm quite certain was caused by this. Not only that, I'm reasonably sure it affects the sound quality too. I've rewired a lot of them as described above and they really do seem to sound better, even when using the exact same wiring. There's quite a lot of possible resistance in all those contact points.

 

[TremoJem]

Agreed and yes I am going to mark up the pcb for future reference, but am buying a plate and mounting switchcraft jacks to it and soldering all connections.

I am so happy to try this damn thing.

 

[Jackie]

I re-soldered all the connections on my PCB just to make sure. Seems pretty solid now.

 

[58boogie]

The best thing to do with this jack plate is first to take off the PCB assembly and throw it as far away as possible. (OK, maybe keep it somewhere safe... just in case you sell the cab.) Then get two standard panel-mount jacks, fit them in the two holes, and wire them in parallel and connect them to the speakers - wired for either 4 or 16 ohms, depending on which you need - with all-soldered connections.

These switching plates are unreliable and can blow your amp's tubes or output transformer. They look like a useful thing to have, but consider that the speaker current has to pass through four switch contacts in the slide switch, four jack switch contacts, and four push terminals, plus multiple PCB solder joints and the PCB traces. If *any one* of these fails in the 16-ohm mode, you've got an open circuit. If certain ones fail in the 4-ohm mode the same thing happens. The jack switch contacts in particular are prone to problems, especially if the cables have been tugged a few times and the contacts get a bit stressed.

Just a bad design - making things much less reliable than they need to be for very little practical purpose. I've seen more than one amp with a blown output transformer that I'm quite certain was caused by this. Not only that, I'm reasonably sure it affects the sound quality too. I've rewired a lot of them as described above and they really do seem to sound better, even when using the exact same wiring. There's quite a lot of possible resistance in all those contact points.

Here is a pic of one burned out, along with black / red wiring designations:

http://www.lespaulforum.com/forum/showthread.php?t=178147

http://i4.photobucket.com/albums/y132/Adpics/IMG_1726.jpg