Humming deluxe circuit

[sdorer]

I built an amp using transformers from a hammond organ. I built a 5E3 circuit and it sounds good. However it hums like crazy when I start it up then it diminishes to a low level what I assume is filament hum. Any idea what the heck is going on?
I've been reading books like crazy for about a year now. Ive built other circuits without issues so I'm not a complete idiot but I am entirely capable of doing something stupid. Thaks for the insight.

[tubeswell]

Hum can come from a number of soucres

bad grounding - internal ground loops (Minimise the number of ground return points by running each ground return via its own separate wire to a common point on the chassis. This helps avid micro-rises in ground potential, which can induce hum

inadequate/bad filtering - are all the filter caps in good nick? (esp the output cap from the CRC filter).

filament hum - try elevating the heater ground to the cathode(s) of the output tubes.

Unwanted induced coupling between the PT and OT - try moving the OT around to get a position of least hum

Unwanted coupling from AC wires into sensitive input grid wires - shield all input wires, and keep AC pairs twisted together to cancel out the EMF surrounding the AC pair. Keep AC wires as far away as possible from signal path wires, and where it is necessary to have them crossing over, only do so a 'right-angles'. Keep signal wires as short as possible, or keep the insulated wires hard up against the chassis - this helps 'eat-up' stray EMR

[Bob-I]

Can you post some detailed pictures? Sometimes the more experienced can spot a problem.

[sdorer]

Actually I was wondering why the humming is so loud for about 30 seconds then diminishes quite a bit. I've read of some of the possibilities that were mentioned in the first reply,thank you but was wondering what would cause the hum to be so loud initially.

[Phil_S]

Actually I was wondering why the humming is so loud for about 30 seconds then diminishes quite a bit. I've read of some of the possibilities that were mentioned in the first reply,thank you but was wondering what would cause the hum to be so loud initially.

Of course, without the amp in front of me, it's pure speculation. I'm thinking the caps charge at about 30 seconds and filtering kicks in. I'm wondering, maybe you've got multiple hum problems that need identification and cure one at a time.

You don't say whether the hum is 60Hz or 120Hz. Hint, the low E on a guitar is 82 Hz. Tune it down to about A# for 60Hz. (That A would be 55Hz). Open A/5th string is 110Hz.

Filament hum will be 60Hz. Poor filtering could well be 120Hz.

[chibby]

I'm not a guru by any means but I remember Mr. Weber saying that the 5E3 is bad humming waiting to happen. It's an oscillation nightmare that sits on the edge of hum all the time. I just can't remember what he said to do about it, but I have the book he wrote that in and will try and find the excerpt from it he wrote about the 5E3 and hum. Think he said early on in his 5E3 building experience he had a few of them that wouldn't even make sound when he turned them on...and they were done right!!!! They would just hum.

[selloutrr]

i had a similar issue in a champ turned out the negative feedback wire was a cold solder. it sounded fine but was much quieter after that over sight was fixed. not sure which chassis you used but the original is very hard to get a solid solder point to the chassis. it took me about 1350-1400 degrees before i could make it flow and bond.

Assuming you are using a 3 prong AC cord chassis ground and not the original cap off the ground switch 2 prong cord.

tubes can play a very large part possibly settling down as the electrons warm up and flow.

does it get better with the chasis in the cab?

are the input jacks closing properly?

not sure how true to vintage you are trying to stay but switching out the resistors to metal film with help. as well as an ceramic caps to orange drops.

the heater wires are twisted and teh wire dressing is neat and seperating signal from power as much as possible.

have you tried moving the wires around with a chop stick to test lead dressing.

[selloutrr]

for reference