5E3 Standby Switch Configuration

[Mojojtm]

Hey All,

I have mostly followed the Stewmac Schematic for building my 5E3. I just finished it .

I hope I have built correctly the point is one on the Stewmac schematics layout the Standby switch is mounted but not connected
On the Mojotone Layout the standBy switch is connected using a .0047uF cap between the standby switch lug and the chassis ground, is that ok?

I am attaching some of my Amp photos

[martin manning]

I hope I have built correctly the point is one on the Stewmac schematics layout the Standby switch is mounted but not connected
On the Mojotone Layout the standBy switch is connected using a .0047uF cap between the standby switch lug and the chassis ground, is that ok?

I believe you are referring to the ground polarity switch, which connects a cap between one or the other of the AC inputs to chassis ground. Original 5E3's had that feature, so the switch is included for cosmetic reasons only (it's non-functional). It is not needed if you have a three-conductor power cable and safety ground.

I like the way StewMac did the input grounds, but the earth ground and the main DC ground should both have dedicated solder lugs bolted to the chassis. You might consider fixing that.

[Mojojtm]

I hope I have built correctly the point is one on the Stewmac schematics layout the Standby switch is mounted but not connected
On the Mojotone Layout the standBy switch is connected using a .0047uF cap between the standby switch lug and the chassis ground, is that ok?

I believe you are referring to the ground polarity switch, which connects a cap between one or the other of the AC inputs to chassis ground. Original 5E3's had that feature, so the switch is included for cosmetic reasons only (it's non-functional). It is not needed if you have a three-conductor power cable and safety ground.

I like the way StewMac did the input grounds, but the earth ground and the main DC ground should both have dedicated solder lugs bolted to the chassis. You might consider fixing that.

Thanks I appreciate that

the power cord ground is on the ground lug under the standby switch, I don't think you meant that

I have another 3 lugs terminal on the other side of the of the PT bolt there I have connected the ground coming from the Turret Board + the ground from the PT + the black heater center tap.

On previous post you said you could ground it but I don't necessarily have to, well... I did it but I didn't put the 2x 100Ohm resistors

So what would I have to correct if you could explain a little easier maybe

[martin manning]

Fender Tweed chassis don't have much room to spare, so I recognize that modifying your amp may be difficult. You certainly don't have to follow all of these rules to get a working amp, but these are the best practices:

In general, it's best to avoid using the transformer bolts for grounds, as they tend to loosen with time.

The PT CT, heater CT lead, and reservoir (first filter) ground should be attached to a solder lug bolted to the chassis near the AC inlet/power transformer end (well away from the input ground). The heater CT (or 2x 100R) can also be attached to this lug.

The safety earth ground wire in the power cable should be attached to a dedicated (no other wires connected) lug bolted directly to the chassis (this attachment does not serve any other purpose).

When not using an IEC power inlet connector (power cable enters the chassis through a strain relief), this lead should be left long enough so that it will be the last one to break if the power cable is pulled out of the chassis.

PS, there is no standby switch on a 5E3. The switch in question here is usually called the ground polarity switch, and that cap is usually referred to as the "death cap." It's intended to reduce noise on the incoming AC. It's not completely useless, but it needs to be the correct type of capacitor, one that will not fail shorted.

[Mojojtm]

Yes I understood very well and thanks I like to learn the best way

i am still on time to modify i have no rush those are learning experience for me the only downside atm is I don't know if I can build more amps since there is shortage of tubes

Thanks

[Mojojtm]

Fender Tweed chassis don't have much room to spare, so I recognize that modifying your amp may be difficult. You certainly don't have to follow all of these rules to get a working amp, but these are the best practices:

In general, it's best to avoid using the transformer bolts for grounds, as they tend to loosen with time.

The PT CT, heater CT lead, and reservoir (first filter) ground should be attached to a solder lug bolted to the chassis near the AC inlet/power transformer end (well away from the input ground). The heater CT (or 2x 100R) can also be attached to this lug.

The safety earth ground wire in the power cable should be attached to a dedicated (no other wires connected) lug bolted directly to the chassis (this attachment does not serve any other purpose).

When not using an IEC power inlet connector (power cable enters the chassis through a strain relief), this lead should be left long enough so that it will be the last one to break if the power cable is pulled out of the chassis.

PS, there is no standby switch on a 5E3. The switch in question here is usually called the ground polarity switch, and that cap is usually referred to as the "death cap." It's intended to reduce noise on the incoming AC. It's not completely useless, but it needs to be the correct type of capacitor, one that will not fail shorted.

Hi Martin

btw you said that the "The safety earth ground wire in the power cable should be attached to a dedicated (no other wires connected) lug bolted directly to the chassis (this attachment does not serve any other purpose)."

Well it is actually done this way, I have a 3 lugs terminal, probably from the picture not visible, the earth ground wire is soldered to one of those lugs and nothing else is attached there, no other wires. This 3 lugs terminal is placed on the bolt that is on the corner that holds tight the PT to the chassis. there are 4 bolts that hold tight the PT against the chassis.

The other 3 lugs terminal, is a bit down on the next bolt down near the 6V6 socket, but not at the opposite side which probably would have been the best place, near the power cord cable hole on the chassis. On the other 3 lugs terminal I have attached the PT CT, heater CT lead, and reservoir (first filter) ground + The heater CT (No 2x 100R). The problem is maybe with the fact that:

You added that that the above PT CT and reservoir (First Filter) "You should attach to a solder lug bolted to the chassis near the AC inlet/power transformer end.

It is not on the chassis but still on the PT bolt and you mention bolts could get loosen with time, true that is probably what I need to modify.

[martin manning]

Here's a picture of a Fender '57 Deluxe from Fender's web site https://www.fender.com/en-US/guitar-amp ... 00100.html. The earth ground is made according to safety regulations, on a dedicated bolt. Note the large loop left in that lead so it will be the last to pull out. The green/yellow wire tucked behind the batten is likely the ground for the back panel.

[martin manning]

I see they have replaced the ground switch with a standby switch, which disconnects the PT CT. The layout diagram is available here: https://www.thetubestore.com/lib/thetub ... ematic.pdf, see screen shot below. Note the PT CT/main filter ground is on the board, not on the chassis, but the PT CT is connected directly to the reservoir cap negative lead, as it should be. The other grounds are scattered on the brass plate like the originals, more-or-less in signal flow order. You can see the dedicated earth ground, and the separate lug for the back panel ground. No transformer bolts are used for grounds, although Fender often did that in the past.

[Stevem]

Why do more folks not wire the standby switch into the ground leg of the recto bridge, or the V+ center tap?

The switches last forever there and never produce popping sounds like when they open & close a DC circuit.

[pdf64]

Why do more folks not wire the standby switch into the ground leg of the recto bridge, or the V+ center tap?

The switches last forever there and never produce popping sounds like when they open & close a DC circuit.

It is DC at the CT.
As has been pointed out previously, in the case of fixed bias supplies derived from the HT, the voltage on bias caps will increase if the CT connection to 0V common is opened. My finding is that about doubling is typical, whether the feed is from the full HT leg or a winding tap.