Slight Hum vanishes when volume or tone cranked .

[showbander]

Just built a 5e3x2...I have a slight hum with no guitar plugged in which maybe a little louder than normal. I'ts definitely usuable but would be nice to have it as good as it can get...

If i crank the volumes or tone to over 3/4 or max th hum Vanishes.

I've Moved output tranny, moved a couple ground connections about and wires etc...still hum.

I'm also wanting to do a check on voltages etc but not really knowing what points i should measure.
If anyone has any suggestion would be much appreciated.

Thanks

[Jana]

Is your input jack grounded when nothing is plugged in?

[showbander]

yes they all are Yana...i have to admit my soldering on the input jacks were a little shoddy and got a little lumpy...Maybe that is the problem even tho its test ok with coninuity.

i will redo those from scratch

Thankyou.

[martin manning]

I'm not a fan of grounding to the backs of pots. If you're going to rework it I propose doing it as shown below.

[showbander]

Thanks Martin, i think the only thing i would need to change looking at your diagram is having the middle cap(20uf ) going to ground by the PT.....rather than having it attatched to the ground buss as it is at the moment

Thankyou.

[showbander]

Oh and change to a 4n7 cap between tone & volume.

[martin manning]

Oh and change to a 4n7 cap between tone & volume.

You mean move the 4n7 from where it was to where I've put it... 4n7 is 0.0047uF. ;^)

[showbander]

sorry My mistake ...! at the moment that 4n7 is going from ground lug on tone control then to the Bus.
I will re-do the grounding scheme how you had drawn it !
Many thanks ...again.

[martin manning]

I missed one cathode ground- see corrected version above. (Edit: No, I didn't... changed back to original.)

[Stevem]

The hum goes away because its being phase canceled when you turn up the controls.
You can hear this going on alot in fender two channel amps with reverb(extra gain stage) you turn up and mess around with contorls on the normal channel when you into the vibato channel and you can kill off most of the hum.
It kills off the hum be it 60hz or 120hz by mixing in hum that phase cancels itself.
The fix is to find the sourse of the hum in the first place and that means to first pin down if its 60hz (transformer or heaters), or 120hz from the B+ section of the amp.

[showbander]

Hi guys, as the weeks have gone on the hum is the same ...ok it's not ridiculous and i could live with it but it is a little annoying because i know its there...
i decided its 50 hz hum after tuning my low e string to it ! i have tried moving the OT and a few suggestions martin said .

Now i forgot to say originally i have unisulated jacks grounding to the chassis and also have a star ground with 3 connections(will this cause a G loop )...should i ditch for insulated jacks or could i just run them to the star ground to save me changing them ?
Regards

[martin manning]

If the hum is 50Hz, and not from induced current in the OT, a likely source is filament circuit lead dress. Can you post a picture of the wiring around the preamp tube sockets?

[showbander]

Hi Martin . lost my camera and could only get crap pic . will try n find it tomo...Earlier i tried reversing polarity of filament wires from 6v6- pre amp but to no avail. Not got round to putting theat back yet tho so it was a little tidier and less wire....all filament wire is pushed to back of chassis a nd reasonably tight i think.
Thanks

[showbander]

Ha ,sorry thats pretty bad photo aint it !

[martin manning]

Good enough for a general idea. That shielded grid wire on the right looks close to the filament wires. What happens if you move that around a bit with a chopstick?