5E3 filament wiring

[Randall]

<Originally posted elsewhere, noob mistake.>

How many of you guys wire the 5E3 as per the Fender schematic? And if not, how do you do it? Specifically, I am wondering about the Fender scheme with one side of the winding straight to ground. Can I go straight across the heaters and lamp without grounding? And can someone explain the virtual center tap resistor scheme a little better? Thanks.

[soundguruman]

In the old days, one side of the heaters connected to ground, it provided a ground buss.
Now days, both heater wires should be installed without grounding. The heater winding floats off the chassis, not connected to chassis ground.
The center tap of the heater wiring connects to ground, or we bypass both ends of the winding with 100 ohm resistors to ground.
If you have an old amp with grounded heaters, you need to rewire it so the heaters are no longer using ground. LIFT the heaters off ground.
Then bypass each end of the winding, with a 100 ohm resistor to ground.
THEN install your grounded power cable / plug. GROUND the chassis to safety ground, from the power service.

[wyatt]

<Originally posted elsewhere, noob mistake.>

How many of you guys wire the 5E3 as per the Fender schematic? And if not, how do you do it? Specifically, I am wondering about the Fender scheme with one side of the winding straight to ground. Can I go straight across the heaters and lamp without grounding? And can someone explain the virtual center tap resistor scheme a little better? Thanks.

The filaments need a reference to Ground for noise and hum purposes. Most modern PT's provide a center-tap for this reference, and with a lo-fi design like a 5E3, that CT is MORE than adequate. But for PT's that don't supply the CT, or when a more accurate center is needed, you connect each side of the filament winding to Ground with two measured and matched 100-ohm resistors creating an artificial center tap. This can be connected anywhere along the filament circuit. Google pics of Clarks' Beaufort chassis and you'll see the 100-ohm resistors added at the lamp fixture, some add them at the end of the wires at V1. I prefer to add them at one of the power tubes....I run a 100-ohm resistor from Pin 7 to Pin 8 and from Pin 2 to Pin 8, this connects the artificial CT to the cathode of the 6V6s and provides a elevated DC ground reference. In theory...less noise...in actuality...with a 5E3, it may be overkill. In a high-gain build like a Soldano, or maybe even a JCM800, where any noise could end up amplified and compressed to full signal strength, I'll always use the artificial center-tap, but I'll install a mullti-turn pot to balance the filaments. (google: "artificial center-tap humdinger")

I would NOT use the traditional Fender unbalanced heater wiring, while it offers a much cleaner layout, it creates to potential for noise and issues. Leo abandoned it for a reason. If you have a CT on the transformer USE the CT, skip the resistors. If no CT, add the resistors wherever you find it easy enough to do so.

[soundguruman]

The filaments need a reference to Ground for noise and hum purposes. Most modern PT's provide a center-tap for this reference, and with a lo-fi design like a 5E3, that CT is MORE than adequate. But for PT's that don't supply the CT, or when a more accurate center is needed, you connect each side of the filament winding to Ground with two measured and matched 100-ohm resistors creating an artificial center tap. This can be connected anywhere along the filament circuit. Google pics of Clarks' Beaufort chassis and you'll see the 100-ohm resistors added at the lamp fixture, some add them at the end of the wires at V1. I prefer to add them at one of the power tubes....I run a 100-ohm resistor from Pin 7 to Pin 8 and from Pin 2 to Pin 8, this connects the artificial CT to the cathode of the 6V6s and provides a elevated DC ground reference. In theory...less noise...in actuality...with a 5E3, it may be overkill. In a high-gain build like a Soldano, or maybe even a JCM800, where any noise could end up amplified and compressed to full signal strength, I'll always use the artificial center-tap, but I'll install a mullti-turn pot to balance the filaments. (google: "artificial center-tap humdinger")

I would NOT use the traditional Fender wiring, while it offers a much cleaner layout, it creates to potential for noise and issues. Leo abandoned it for a reason. If you have a CT on the transformer USE the CT, skip the resistors. If no CT, add the resistors wherever you find it easy enough to do so.

Yeah, if one lead of the heater wiring is grounded, it has to be taken off the chassis entirely.
Because, when we add a grounded 3 wire power cable, you will have severe noise problems.
But the heaters will work fine, without being connected to the chassis.
And then last, balance the heater winding to ground, thru the two 100 ohm resistors.
We have to do this to every amp with the grounded heaters: Mod the heater wires so that the one side does not connect to the chassis anymore.
If the transformer has a heater center tap, then ground the center tap. Unfortunately, older amps do not have this CT for the heaters, so we use resistors instead.