5E3 Grounding

The original Fender layout includes six main chassis grounds:
AC ground through the death cap switch
Power transformer center taps (green and red-yellow)
First power cap and 6V6 R/C
Second and third power caps
Preamp V2 R/C
Preamp V1 R/C
There are three faceplate grounds: the Tone and Volume pots, and the four input jacks. The tone and volume parts are grounded to the faceplate through the pot body. The inputs are also grounded through the faceplate.
Upgrading to a three-prong cord adds another chassis ground.

Transformer Bolt Grounds

The center tap and first power cap chassis grounds were changed to solder lugs on the transformer bolts in the brown and blackface era.
This presents several problems due to faulty connections caused corrosion and loose bolts. Chassis bending occurs in larger amps with heavy transformers.

Shocks and Tingling

In the 50’s, 60's and into the 70's people often got shocked when touching two different devices. It happened so often that it was common practice to touch the guitar strings to the mic stand and look for sparks or listen for static.

Two and Three-Pronged AC Cords

These “shocking” issues were caused by two-prong plugs. One side was hot and the other was the return. Wood cabinets were used to isolate the metal chassis.
Later the standard for one larger prong was implemented, which was then replaced by the three-prong plug.

The Death Cap Switch

The so-called “death capacitor” connected one side of the two-pronged AC cord to the chassis, with a switch to change sides. Fender brown and black faced amps changed this to a three-way switch on the back of the amp.
The idea was to use the non-shocking side. With three-prong cords, the middle position (disconnected) is appropriate.
Removing the death cap, however, is preferred.

Isolation Transformers

Some early amps connected the AC mains directly to the tube heaters. This is a dangerous design because tube failure might connect the AC directly to the chassis.
The power isolation transformer was implemented, followed by 6 or 12 volt heaters.

Understanding Grounding

The old style of amp design considered the idea that current flowed into the tubes and out through the chassis to the return. The chassis had ground current. The idea was to separate the ground currents for low noise.
Modern circuit board design has similar practices with separate ground planes for digital and analog circuits.

Input Jack Grounding

Fender tweed, brown and black face era amps grounded the inputs through the faceplate. The connection is through the input jack washers, which are subject to rust and corrosion.
Plastic chassis isolation washers are often used on the input jacks of HiFi tube amps, which is also used in modern Fender amps.
One good idea is to ground all the input jacks to a separate chassis ground in the corner so that it is far away from the other grounds.

Power Supply Grounding

If we look at a 1965 Blackface Fender Deluxe Reverb Chassis, the power supply has three separate grounds:
Power transformer center tap (red/yellow) and heater center tap (green/yellow); bias board;
AC ground (green).
The power supply capacitors (doghouse) has a separate ground (black) between the bias pot and circuit board.

The Ground Plate

In some blackface amps, the cathode caps on the board each had a separate ground wire to the front panel copper or brass grounding plate.

Copper vs Brass

Copper is the better conductor, whereas brass is stronger, which is why the input jack grounding plates are made of brass (usually .01 thick for easy bending and drilling).

Ground Buss Wire

Many amps have a buss wire for grounds, typically tinned copper. In guitars, this is soldered across the pots. Some amps also have the ground buss soldered across the pots, but it makes replacing pots difficult.
A better solution is to lay the buss wire on the chassis and solder at either end.

List of Grounds

For the 5E3 clone, there are five separate chassis grounds:
AC Cord ground (green)
Power transformer center tap and heater center tap
Power supply first capacitor (or doghouse in larger amps)
Tone stack and preamp capacitors (buss wire or ground plate)
Input jack grounds

Tools

X-Tronic Model 9060-PRO-X • 200 Watt Stained Glass Soldering Iron
https://www.amazon.com/gp/product/B09MV199ZW/