Issues with 5E3amp

[xtian]

Out of standby mode it still hums. Is that normal for a 5E3?

No, not "normal." Common, but not normal. Grounding scheme is critical. So is the orientation and placement of the PT vs OT.

[guile]

That fixed a lot! I need to get glasses (seriously, I'm of that age).
Thanks very much everyone.

Amp is much quieter and no more strange clipping (tested it loudly, sorry neighbours..).
Out of standby mode it still hums. Is that normal for a 5E3?

Hum is normal in most amps, does it go down with volume, change with specific pots etc? sometimes it's lead dress, sometimes it's a heater imbalance, sometimes it's just the normal hum for an amp at full volume (If that was how you were playing it). Were you using single coil pickups? Does the hum exist w/ nothing in the input? That could just be the guitar.

You can try replacing the 100 ohm resistors to ground on the heater circuit with a hum balance pot and see if you can dial it away. That's usually a subtle change though.
Some of your leads are a bit long and hanging around loose in the amp, this gives room for hum and noise transfer between wires. you can get a wooden chopstick and try moving the leads around and see if the hum dissipates.

Hum is a nefarious enemy

~Phil

The hum is there when of standby and nothing plugged in.
When plugged in (either inputs) I don't hear any change other than normal single coil 60 cycle hum etc. I dont think it's the guitar(s).
The pots add normal hiss and hum but do not change the initial hum.
I already installed a humdinger and this filters some hum.
Dressing the leads differently does not yield any difference(!).
I noticed that the hum changes in intensity when I move my hand near (not on) the open amp. This does not happen when I use a well grounded wall outlet.

Could it be the power tube resistor. Mine is 220 ohm and this may be too hot...

[guile]

Out of standby mode it still hums. Is that normal for a 5E3?

No, not "normal." Common, but not normal. Grounding scheme is critical. So is the orientation and placement of the PT vs OT.

Thanks
Maybe you see any anomalies?

https://www.flickr.com/photos/115176149 ... 1061564087

[pdf64]

You look to be using the chassis as a conductor for circuit common 0V, and have several connections to implement that. Perhaps the arrangement used is not good, where did you get it from? Also I don’t think that it is good practice to rely on a soldered connection to a single pot body as a means of providing a connection to the chassis metalwork.

The mains safety ground connection looks to be soldered, and poorly done. There’s only 1 safety critical connection in an amp, please do it correctly.

If you think that some of the wall electrical outlets in your house have bad grounds, then for safety’s sake get them fixed and ensure that they aren’t used in the meantime.
We’re on 230Vac mains in Europe, electrocution has far greater risk of fatality than it does in 120Vac regions.

How is the hum affected if the amp is operated without tube in V1 and V2? How about if a tube is then put into V2?

[sluckey]

The mains safety ground connection looks to be soldered

Also, your chassis looks to be aluminum? If so, you cannot solder to aluminum. Sure, it will "stick" but it ain't a soldered connection. You can take a small hammer and screwdriver and gently tap until that solder blob pops loose. The only way to make an electrical connection to an aluminum chassis is to bolt it down. Good mechanical equals good electrical.

If your chassis is steel then you can solder directly to it. But not with a typical iron. You need a big wattage iron or gun and use flux.

[guile]

Thanks.

I got the kit from a reputable source.

It's not clearly visible on the photo but I can assure you that the mains safety ground is very firmly soldered to a pre- roughed up (steel) surface with a big (clumsy) wattage iron, including flux, so well flowed.
I tried to take it of by force, but it stays firmly attached to the chassis.

I fixed the connection to a single pot body (because of the voltage build up and hence sensitivty to radiowaves etc., isn't it?).

Same voltage here in the Netherlands (240 max). It's common here that wall outlets are not grounded. They're protected with an earth leakage circuit breaker system. Wall outlets in kitchens, bathrooms etc. are of course grounded.

When the amp operates without tube in V1 and V2 it's completely silent. When a tube is put in V2, same hum..

[martin manning]

When the amp operates without tube in V1 and V2 it's completely silent. When a tube is put in V2, same hum.

So V2 is likely to be a source of the hum. See if moving the pin 2 grid lead away from the heater wires makes any difference. In general I think your heater wiring needs a bit of tidying up. Is the hum 50 Hz or 100 Hz?

[guile]

I made a little clip of the amp (please don't mind burned thumb)

https://www.youtube.com/watch?v=h56IoVuqFHQ

[martin manning]

50Hz hum. The popping when you touch the chassis with your finger suggests it is not well grounded.

[Phil_S]

It is 50Hz hum. As Martin says, the heater wiring can use some clean up. Keep heat wires away from signal wires. In the bottom picture, the blue wire passes next to or through the green heater wires. I would rework that wire. Unsolder the end on the socket close to the jack. The run it on the other side of the tube socket, passing near the circuit board. If you can get it to stay in the fold of the chassis, that looks like a good place for it.

This one may not be a problem. Leave it for now. The red wire (B+ supply) is threaded through the green pair of heater wires on the left. Unsolder at the socket/resistor. Run it above the green wires and reconnect. It may not be long enough. You may need to replace the whole wire.

In the other picture, the yellow wire is threaded between the twisted green wires. You said there is no hum when you pull V1 and V2. This one is likely the first thing to fix. Rework the heater wires so they are touching the chassis. Lift or bend the yellow wires so they are away from the heater wires.

[martin manning]

Do you have more preamp tubes to try? Failed heater-cathode insulation can cause hum like that.

[alkuz1961]

I think it could be a big problem at some point.

2019-09-28_20-15-26.jpg

If you accidentally pull out the connector you'll have to buy a new transformer.

But if you already installed the output jack with switching, then a good solution would be to replace this blue wire with a 10-15W 16ohm cement resistor.

[sluckey]

I think it could be a big problem at some point.
If you accidentally pull out the connector you'll have to buy a new transformer.

That's how I wire all my main speaker jacks. So does Fender. I'm comfy with it.

[alkuz1961]

That's how I wire all my main speaker jacks. So does Fender. I'm comfy with it.

Does your transformer also short onto the ground when you pull out the speaker?

[sluckey]

That's how I wire all my main speaker jacks. So does Fender. I'm comfy with it.

Does your transformer also short onto the ground when you pull out the speaker?

Yes. A short is fine. Open is bad.