5E3 Build Ground Hum (Probably Loop) Issues

[Kitarist]

So i just built another 5E3 build and this time i have Ground hum issues.

I'm using Ceriatone Style Grounding. http://ceriatone.com/images/layoutPi...3Ceriatone.jpg

Also when i put guitar into the input jack the ground hum amplifies.

Anyone got a clue what it could be? I tried moving cables around etc...

I'll post some pics when i can

[pdf64]

I'm not sure that grounding scheme is good.
The 0V side of the reservoir cap should best be connected directly to the CT of the HT winding, as it will carry heavy ripple current.
Then from that terminal to a suitable 0V common point, eg Y.

[Chuck H]

What he said ^^^^^^^^^^^^^^^^^^^^^^

Not an ideal grounding scheme at all. Also, since this is a new build there is still the possibility of a wiring error or cold joint that may be preventing a ground.

[Kitarist]

Could you draw it so it would be easier or tell me which layout grounding should i use?

Thanks!!!

[Chuck H]

Could you draw it so it would be easier or tell me which layout grounding should i use?

Thanks!!!

Nope. Too much trouble. The image you posted is the standard way to wire a 5e3 AFAIK. A better way is to use a two star ground scheme. One for the preamp and it's filter grounds near the input and one for the power amp and the main and screen filters with the PT CT's on that end of the chassis. But if you're grounded as per the image you posted then perhaps you would get some hum. Not the bad hum you describe though. There shouldn't be any ground loops unless you have made redundant grounds or daisy chained grounds on the board for convenience. Both are no no's and should simply be undone. If that doesn't solve for the hum it isn't a ground loop. Well... There is technically always some looping due to the chassis being the ground. But nothing like what you describe.

Something to check would be the first preamp tube. I fussed and screwed around chasing a hum for a few hours on a new build once. I didn't suspect the brand new tube I'd installed. But that was the cause. And it's getting more and more common to get hummy tubes new out of the box. So common anymore that I always buy extra tubes for a build so that I won't get stuck without a working tube. Which WILL happen. If you only buy what you need, at least one of them will be bad. Probably more IME. So replace your first preamp tube with a known quiet one just to check.

If that doesn't fix it, it's still possible you have an actual ground fault somewhere.

[Kitarist]

Long time no reply was really busy with other things and just decided to let this project rest for a while.

Because i wa suspecting the plastic jacks i went and got the "original" jacks that were used in those kind of amps.

Well the hum is always present now whetever the guitar is plugged in or not and also increases with volume.

Here are some pics:

http://imgur.com/a/orc0W

[pdf64]

Yikes, I forget how horribly cramped a 5E3 chassis is.
I think that the heavy gauge wire used for the heaters may have made a tricky job even more difficult.
The chassis glare from the flash in the 1st pic isn't helping, but really it's so cramped that it's hard to trace anything out.

Have you tried subbing in known good tubes?

Do the volume controls affect the hum if V1 is removed?

It would be helpful to report the results of a voltage survey under idle conditions, ie Vdc / Vac (as appropriate) at each tube pin, PT, HT caps.

[Kitarist]

I did forget the say the hum is present but the amp behaves normal when i plug the guitar on it and play it but hum is always present and also increases when i increase the volume. The hum is really loud tho. I think its probably some silly ground loop issue hm...

[Kitarist]

Here is an album with more detailed pictures:

Imgur: The most awesome images on the Internet

[pdf64]

With the amp disconnected from mains and de-energised, what is the resistance between any point on the 6.3V heater system, and the chassis 0V?