From Our Mailbag: Question on the MOD 102 Amp Kit

By Guitar Kit Builder
Sep 26, 2011
in Guitar Kit Builder - Amplifiers

GKB reader Dave F. wrote to ask the following about our review of the MOD 102 amp kit and the modification made by Casey4S:

"Wow that is really cool how you made the chassis and the fantastic building skills. My question concerns the use of the grounding jack where you stated ...

"I used a Switchcraft 12A type grounding jack for the speaker out because the output transformer (OT) can be damaged if you have no load present (nothing plugged in) when the amplifier is on. With a grounding type jack the output circuit is just grounded and doing no harm if there is no speaker plugged into the amp ."

For a newbie like me I know these jacks have a ground, switch, and signal tab. Can you tell me exactly how they are connected. I know positive to signal and negative to ground but what then? Thanks for any help."

Switchcraft 12A Jack Details

Before we hand this off to Casey4S for the answer on the mod 102 amp kit we want to cover the details of the Switchcraft 12A jack.

Take a look at the drawing here from Switchcraft's catalog and you'll see that it has three connections - the tip, sleeve and shunt. The tip and sleeve are the two traditional speaker connections. The shunt is the third terminal and connects to the tip until a plug is inserted. With plug in, the shunt is disconnected. This makes it ideal in an application, such as the way that Casey4S used it, where we want to ground the tip until a speaker connector is plugged in. OK, over to Casey4S...

Mod 102 Amp Kit Answer

Casey4S responds: Dave, check out these photos. With the jack showing all three terminals on top, the black wire goes on the far left terminal, the green goes on the far right terminal, the center is a short wire to the nearest convenient chassis ground. (green cloth). mod 102 amp kit jack 1