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Vintage threads from the first ten years

previous: Howard Hum trouble with 6G15 Reverb kit -- 8/1/2004 12:28 AM

DANGER! Will Robinson!

8/1/2004 6:52 PM
MBSetzer	DANGER! Will Robinson! You differ too much from the vintage unit. Difference No. 4 is the potentially deadly one. Never, ever, connect either the hot or the neutral AC supply wires to the chassis. There are usually at least 15amps of current at 120V available on those wires before a circuit breaker in the building will be tripped. That's why you just use the incoming hot & neutral to connect only to the primary of the PT, that's a coil all it's own which is isolated from everything else in the amp. The amp then gets its power from the PT secondary, which is also isolated from everything else except when you connect the B- of your HV DC power supply to the chassis and/or earth ground for reference. You're expected to have a relatively small fuse on one of the incoming power leads, like 1/2 amp or less for a reverb unit, along with a switch, and that's conventional wiring. The neutral connects to earth somewhere in the building, not inside equipment. The green dedicated earth lead is the only one from the power cord which is supposed to be connected to the chassis. After you correct this safety defect, it may also reduce the hum. If still not low enough in hum, you may consider using an isolated phone jack for the output of the reverb unit. This is the way Fender has it on my SF Tube Reverb, which is not exactly a 6G15, but you could compare those schematics for differences to see if it can be helpful. Mike

8/1/2004 6:52 PM

MBSetzer

DANGER! Will Robinson!

You differ too much from the vintage unit.

Difference No. 4 is the potentially deadly one.

Never, ever, connect either the hot or the neutral AC supply wires to the chassis.

There are usually at least 15amps of current at 120V available on those wires before a circuit breaker in the building will be tripped.

That's why you just use the incoming hot & neutral to connect only to the primary of the PT, that's a coil all it's own which is isolated from everything else in the amp. The amp then gets its power from the PT secondary, which is also isolated from everything else except when you connect the B- of your HV DC power supply to the chassis and/or earth ground for reference.

You're expected to have a relatively small fuse on one of the incoming power leads, like 1/2 amp or less for a reverb unit, along with a switch, and that's conventional wiring.

The neutral connects to earth somewhere in the building, not inside equipment.

The green dedicated earth lead is the only one from the power cord which is supposed to be connected to the chassis.

After you correct this safety defect, it may also reduce the hum.
If still not low enough in hum, you may consider using an isolated phone jack for the output of the reverb unit.
This is the way Fender has it on my SF Tube Reverb, which is not exactly a 6G15, but you could compare those schematics for differences to see if it can be helpful.

Mike

Replies:

DD Never, ever, connect either the ... -- 8/1/2004 7:08 PM
Howard Thanks for catching that. An easy ... -- 8/1/2004 10:19 PM