5E3 Build Hum

[maxupp]

Hey, it's me again...

My speaker turned up, and unfortunately the hum isn't gone, and it's still very noticeable. made a quick video:

It's still there when I pull V1, but goes away when I pull V2, so I'm pretty sure it's in the preamp somewhere, maybe grounding issues? I'm in Europe, so 50Hz mains, and the hum is at 100Hz.

I rewired the input jacks according to Robinettes schematic, and previously shortened and spaced the leads to the preamp tube sockets.

I am thinking about lifting the ground leads from the pots to the board, since the pots should be well grounded via toothed washers.
But before doing that, I was hoping for some input from you guys...

Pics of the wiring/grounding: https://photos.app.goo.gl/EXotPB1DULk1B2XP6

[tubeswell]

Looking at all those different wires going onto the pot cases, I'd say the grounding needs revisiting

[maxupp]

I just lifted the wires going to the pot cases as an experiment. The hum did go away to like 90%, but when I touched the ground wire back to the pot with a plastic probe, it arced a little. I'm pretty sure that shouldn't be happening, right?!
The ground side of the filter caps is wired to the green and yellow wire from my mains transformer.
Here's where there might be an issue I think. The green/yellow is the center tap of the 6.3V used for the heaters. If I'm not mistaken, that isn't a true ground at all, so the center tap was only grounded via the pots? Pretty confused right now.,


The way I have set it up is:
Double Yellow to the rectifier heater
Double Red rectifier high voltage AC in, Center tap to standby switch.
Double Green running to pilot light and heaters, center tap to board ground.
Mains Blue/Black running to power switch, white heatshrinked off.

Here's the schematic of my transformer:

[sluckey]

I just lifted the wires going to the pot cases as an experiment. The hum did go away to like 90%, but when I touched the ground wire back to the pot with a plastic probe, it arced a little. I'm pretty sure that shouldn't be happening, right?!

Yes, it should have arced because you have your filter caps connected to the back of the pots. Bad idea!

Here's a link to a proven 5E3 layout. Make your amp look like this, especially the grounds, and you hum issues should go away.

     https://robrobinette.com/images/Guitar/5E3P_Build/5E3_Deluxe_Amp_Layout.pdf

[maxupp]

I just lifted the wires going to the pot cases as an experiment. The hum did go away to like 90%, but when I touched the ground wire back to the pot with a plastic probe, it arced a little. I'm pretty sure that shouldn't be happening, right?!

Yes, it should have arced because you have your filter caps connected to the back of the pots. Bad idea!

Here's a link to a proven 5E3 layout. Make your amp look like this, especially the grounds, and you hum issues should go away.

     https://robrobinette.com/images/Guitar/5E3P_Build/5E3_Deluxe_Amp_Layout.pdf

That means I should take the legs away from the cases of the pots as well?

[sluckey]

Here's a link to a proven 5E3 layout. Make your amp look like this, especially the grounds, and you hum issues should go away.

[maxupp]

I hacked together a split ground bus like you guys suggested, see the preamp section below.
Not sure how to do the chassis ground for the power amp section. Is a screw-on lug prefarable over a solder joint?

[sluckey]

Not sure how to do the chassis ground for the power amp section. Is a screw-on lug prefarable over a solder joint?

I prefer screw with lug and kepp nut. Most people don't have a soldering tool that's powerful enough for a soldered joint. An of course you cannot solder to aluminum.

[RadioComm]

Most people don't have a soldering tool that's powerful enough for a soldered joint. An of course you cannot solder to aluminum.

If needed though, ie working on old Fenders, a Weller soldering gun does the job.

[dude]

Two chassis grounds like the photo Sluckey sent, the power amp side (e-caps, cathode bias ground, PT CT, PT filament ground) get grounded  near PT or leg of PT. the other chassis ground gets grounded at the input side, near the jack you plug your guitar in. Use a nut and bolt, the bus bar should be connect at the bolt at the preamp end only and not connected to the main star ground near the PT.

Just trying to clarify you read the photo correctly.   

[maxupp]

I redid the grounding completely now, according to the schematic. It's an absolute hackjob with all sorts of mismatched wires, but it worked and the hum is gone.
I will redo it once the pushback wire I ordered arrives.

Now all that remains is a slight hiss that isn't all too bad, and the nagging feeling that my low DC voltages are robbing me of some volume and punch. I had ordered a second 5Y3S rectifier, and it gives the same B+ voltage, so I suppose it's just the voltage the mains tranny delivers...

[dude]

List the voltages

[sluckey]

If needed though, ie working on old Fenders, a Weller soldering gun does the job.

Yep. I have that one and it's big brother too...

     https://www.amazon.com/Weller-D550-Dual-Professional-Soldering/dp/B00002N5LO/

[maxupp]

List the voltages

My apologies, had done so in my other post:

[bmccowan]

Well, those are the about the voltages I shoot for with a 6V6 build. If they creep up much higher I try to bring them down. Its a tone thing, not a max volume thing. Most Fender schematics have voltage listings, but not the 5E3. I think the 5E3 should sound fine in that range, but which PT are you using? There is a lot of variation - even in Fender factory amps. I think that if you search you will find projects with plate voltage ranging from around 325 to near 400.

[dude]

5E3 B+ range is about 355vdc, which is about what you have.  The 5E3 is about 15 watts, loud enough to gig if your drummer isn’t real loud. Some  hiss is normal when turned up but playing you can’t hear it. You could try chop sticking wires around for the less hiss.
You got the noise issues fixed, you’re ready to jam, looks like a good job, cheers.
BTW, a lot of builders de-fart the 5E3 buy lowering some coupling cap valves.

[bmccowan]

cutting back on broccoli, cabbage, and Brussels sprouts will also help with the de-farting.

[tubeswell]

cutting back on broccoli, cabbage, and Brussels sprouts will also help with the de-farting.

And beans

[bmccowan]

Oh yes, the musical fruit.

[tubeswell]

here you go

[72Blazer]

still funny 50 years later

[bmccowan]

I gave my 7 year old grand nephew a copy of Freddy the Farting Snowman. It's his favorite and he did an oral book report on it at school. His parents are so proud.

[dude]

One sentence in a post brings on "Blazing Saddles" flick scene,  . You guys are getting older by the minute, I guess I'm in that group too. Cheers, and watch those beans..! 

[Mike_J]

I tried various rectifier tubes to get the tone I wanted. Settled on a 5U4GB if I recall. It has an about 60 volts less B+ than the 5Y3 but I liked the tone better. Might have beefed up the preamp voltages by dropping a few resistors values to get the preamp more in line with what the 5Y3 voltages were but I don’t think it made a huge difference.


As previously mentioned what did help the amp considerably was putting a switch on one side of the V-1 cathode to be able to adjust for the problem previously mentioned by many on this post.


Amp is plenty loud enough.

[tubeswell]

… nagging feeling that my low DC voltages are robbing me of some volume and punch. I had ordered a second 5Y3S rectifier, and it gives the same B+ voltage, so I suppose it's just the voltage the mains tranny delivers...

What sort of speaker are you using?

[maxupp]

… nagging feeling that my low DC voltages are robbing me of some volume and punch. I had ordered a second 5Y3S rectifier, and it gives the same B+ voltage, so I suppose it's just the voltage the mains tranny delivers...

What sort of speaker are you using?

Jensen P12Q, admittedly not the most efficient speaker.

[bmccowan]

I tried various rectifier tubes to get the tone I wanted. Settled on a 5U4GB if I recall. It has an about 60 volts less B+ than the 5Y3 but I liked the tone better.

A 5U4GB will provide higher, not lower B+ voltage than a 5Y3. Unless the 5Y3 is one of the bogus Sovteks they produced a while back. A 5U4 might be worth a try in that amp. But I am wondering if you perceive a lack of punch/volume, or it you are just looking at the numbers?