Another 5e3 Hum Question

[rockybottom16]

I've got my recent 5e3 build to be pretty quite when idling with nothing plugged in and the volumes down, but I just tonight noticed that when you turn up the volumes it has a hum that goes up as the volume goes up. The 5f2a that I just completed has a little hum at idle, but there's no change when you turn up the volume. Is this just because of the circuit differences, or is my 5e3 still fubared?

[Leif H]

I've got my recent 5e3 build to be pretty quite when idling with nothing plugged in and the volumes down, but I just tonight noticed that when you turn up the volumes it has a hum that goes up as the volume goes up. The 5f2a that I just completed has a little hum at idle, but there's no change when you turn up the volume. Is this just because of the circuit differences, or is my 5e3 still fubared?

I had major hum issues, now it's rather quiet, but the Hum comes up with the volume, however, I thought this was a normal issue, as my other amps have had that similar hum.

I have to say that I think this circuit is probably noisier than what is the norm due to the volumes being rather interactive and that the tone control acts differently than any other amp I've used before. I feel that the tone at 12, is normal, and the tone at 0 acts like more of a treble cut?

And the tone control seems to also increase the hum, or accentuates that freq.

[tubeswell]

Have you got the heaters elevated (to the output tube cathode(s) for example?)?

[rockybottom16]

Heaters not yet elevated - it's on my to do list. I did find part of the reason, though. Over the weekend I installed a switchable V1 cathode bypass cap. I'm not sure why, but when the switch was running the 4.7uf/820 ohm configuration, the amp's hum got considerably louder. Switch it back to the stock 25uf/820 ohm circuit and most of the hum went away. The difference in sound was so subtle that I just undid the mod and now I'm happy again. Maybe this weekend I'll elevate the heaters. By the way, can I elevate the heaters the same way on my 5f2a build (filament CT to 6v6 cathode)?

[loudthud]

All tube amps have small amounts of hum. Is the hum 60Hz or 120Hz? Using a 12AX7 or 12AY7 for the first preamp tube? Did you use coax for the inputs and wires to/from the pots? Do you have some kind of metal foil on the back panel closing up the chassis? Willing to re-build the whole amp to get rid of the hum?

[Leif H]

....Willing to re-build the whole amp to get rid of the hum?

That's a good point, I feel I have just about re wired the whole amp with my first build.
But as I'm an old school kind of guy, I expected it to be a bit of a struggle.

Having everything fall into place, with no issues, I wouldn't have learned anything. It made it a bit interesting, and the people on this board helped a lot.

Now, I just need some time to get out and jam!l

[RWood]

Did you use a switching jack on the input?

If not, that will contribute hum when nothing is plugged in and the volume is raised.

If you did, double check that you wired it correctly. With nothing plugged in the grid of the input tube is grounded, which should silence it at any volume.

You might still hear some power amp noise, but none from the preamp if the input is grounded.

RWood

[rockybottom16]

Thanks for the input jack suggestion. I did use switching jacks, but upon inspection I found the switch wasn't making a good contact with the tip. A light brush with some emery cloth and a little contact cleaner solved the problem. The volume controls no longer affect the hum. Yahoo!