hummm issues

[Leif H]

I figured I'd move to this forum to get some help.

I've built a 5E3, I used Fender's / Webers layout from parts sourced here and there. Cap's from weber, as are the pot's.
Resistors are from my local electronics supplier.
Tubes are NOS, or used from a Filmosound amp I had started to mod into a 5E3, but I decided I wanted two channels.
Chassis and eyelet board are from ebay.

The layout went well, soldering it was a breeze.

I powered it up, and had some hum, actualy lots.
I swapped tubes, to no avail. the hum seems to disappear when I pull the PI, but not the pre amp tube.

I moved the grounds from the brass plate, to a star ground as follows;
Bias, 1st & filter caps have a shared ground
2nd & 3rd filter caps shared ground.
Ground from tone, Volume and jacks
separate ground from the bypass caps for V1 & 2.
Separate ground from output jacks.
PT and mains ground all tied to the chassis.

I've still got hum. In fact, it seems that the tone seems to really make it worse when turned up.

I tried removing the tone stack, which just made it worse.

I put a piece of co-ax from the Volumes to the PI tube, and that did nothing.

Thoughts?

[MWJB]

Tone & vol pots want a buss wire soldered to the backs of the pot bodies, this terminates at Normal/Mic 1 input jack ground terminal. Also terminating here should be V1 cathode resistor & bypass cap, V2 cathoder resistor & bypass cap, preamp filter cap.

Ground everything elso to a PT bolt, using one wire for each component.

Your heater wires look a bit wild from this angle, keep these away from grid wires to the preamp tubes.

How are the PT & mains grounds tied to the chassis, with a nut, bolt & solder tag, or did you solder to the chassis?

Can we see the tube socket wiring?

[MWJB]

Shielded wires to preamp tube grids should be grounded at one end only, heatshrink the other end to avoid shorts.

[Leif H]

Tone & vol pots want a buss wire soldered to the backs of the pot bodies, this terminates at Normal/Mic 1 input jack ground terminal. Also terminating here should be V1 cathode resistor & bypass cap, V2 cathoder resistor & bypass cap, preamp filter cap.

Ground everything elso to a PT bolt, using one wire for each component.

Your heater wires look a bit wild from this angle, keep these away from grid wires to the preamp tubes.

How are the PT & mains grounds tied to the chassis, with a nut, bolt & solder tag, or did you solder to the chassis?

Can we see the tube socket wiring?

To clarify, should I take the cathode resistor & bypass cap to the Jack ground terminal of normal input 1? and the other end of that ground buss running to the star ground.
I've bolted the grounds to the chassis, and soldered the wires into ring terminals bolted to the chassis.

The heater wires are run up and around the lip in front of the output jacks, then I tried to get them up and over the other wiring to the input tubes.
I'll get a picture of the tube wiring later...

[MWJB]

"To clarify, should I take the cathode resistor & bypass cap to the Jack ground terminal of normal input 1? and the other end of that ground buss running to the star ground." Normally the other end of the grounding buss is not connected to anything, try it like that first, still got an issue then try it tied to the star ground.

"I've bolted the grounds to the chassis, and soldered the wires into ring terminals bolted to the chassis." Good.

[MWJB]

Does your PT have a 6.3VAC heater centre tap wire (usually green/yell), or did you use 2x100ohm resistors as a virtual ground?

[Leif H]

Does your PT have a 6.3VAC heater centre tap wire (usually green/yell), or did you use 2x100ohm resistors as a virtual ground?

No I didn't do the virtual ground, and I don't have a centre tap...

where is the bst place to put this? terminal strip mtd. on chassis?

[loudthud]

Are those the 100 ohm resistors for the virtual center tap on the 6V6 sockets?

OOOPs took too long looking at the picture.

[MWJB]

Couple of options, assuming that heaters are wired as a "twisted pair" - e.g. wire from pin 2 of one 6V6 goes to pin 2 of the next & then on to ONE side of the preamp tubes (either 4 & 5 tied together, or pin 9), the other heater wire goes to pin 7 of the 6V6s & the OTHER side of the preamp tubes...

Mount them on the pilot light, each resistor goes to a terminal. Free ends may be grounded to the pilot ligt bracket that screws to the chassis (remove bracket from the chassis & use a big hot iron) or free ends can be tied together & run a ground wire from the junction to the PT bolt ground.

Or, mount them on the tube socket, one from 6V6 pin 7, the other from pin 2, free ends tie to pin 8 (cathode resistor & cap). This provides a dc bias to the heaters & can reduce hum.

[Leif H]

Here's the tube's wiring, the heater's wiring is getting messier as I prod...

[Leif H]

Are those the 100 ohm resistors for the virtual center tap on the 6V6 sockets?

OOOPs took too long looking at the picture.

I swear that chassis has that effect on me too. I've been looking too long at this too... I'm dreaming about it, seriously.

I play so much better in my dreams!

[MWJB]

Yellow speaker wire should go straight accross the chassis floor, not loop around tube sockets. You have yellow & green wires from the OT...seems unusual, what does the legend say as regards OT taps?

Ther appears to be a jumper wire accross the main speaker jack...please confirm?

If you do the heater wires last it's best to wire them "up & over" the tube sockets, rather than flat against the chassis floor (which you would do if wiring the heaters first).

[MWJB]

No, they are 1500ohm grid stoppers.

[Leif H]

Yellow speaker wire should go straight accross the chassis floor, not loop around tube sockets. You have yellow & green wires from the OT...seems unusual, what does the legend say as regards OT taps?

Ther appears to be a jumper wire accross the main speaker jack...please confirm?

If you do the heater wires last it's best to wire them "up & over" the tube sockets, rather than flat against the chassis floor (which you would do if wiring the heaters first).

They yellow wire on the speaker output is the ground, I was out of white.
the second yellow you think you are seeing is just a reflection. (I'm sorry I'm not much of a photographer).

The output wires are greeen / black and the jacks are wired according to the layout (webber, fender).

I'm going to re wire the heaters tonight as they are now a mess. And keep them spun tighter and above the tube sockets as suggested.

[MWJB]

If the output wires are green & black, you don't need the yellow wire. The jacks ground through the chassis connection. You are most likely causing a ground loop hum.

I am confused by your output jack wiring, it doesn't match the Weber layout & the Fender layout has no detail in this respect (you would be very lucky to build a properly functioning amp based purely on Fender schems & layouts, they are service documents, not detailed "how to" instructions).

According to the Weber layout, with the upright tip contact of the jack socket farthest from you (as they appear in your photo), the terminal to the LH side of the main speaker jack (Tip) gets the green wire from the OT, this wire is then continued to the ext jack tip terminal. The terminal farthest to the RHS (sleeve) gets the black wire & a jumper to the middle terminal (switch) on the main speaker jack. DOUBLE CHECK this, the sleeve/ground terminal is easy to spot because you can normally physically see the terminal connecting to the centre ring of the jack.