Faint ringing/hum after being powered on for a few hours [resolved]

[watonwak]

Hi, I now have a mostly well working crack,  stock apart from the diode mod and an Alps blue, but before I install the speedball I have noticed that after it has warmed up for a while it develops some noise. This temporarily resolves with a sharp tap on the top plate. I have already reflowed most of the joints. I previously had a hum that was the grounding not being great but this sounds a lot different, could it be tube related?

Thanks, Euan

[Tom-s]

If the reflow failed, voltages are all good, and the problem persists, it's time to narrow it down to specific solder joints. What you could do at this point is chopstick around with a cheap pair of headphones connected.

1. Turn Crack upside down with cheap headphones plugged in. 2. Get wooden chopstick. 3. Turn on crack and leave it for an hour. 4. When the noise is present, poke at ground path joints and other components to check if you can get the sound to change at certain points. 5. If so, great succes, reflow these joints when all is cooled down.
6. If not found, check with other tubes to see if it's a tube problem (for recommendations, see tube rolling thread).
7. If all previous fails, check out PB diode config on ground.

[watonwak]

Thanks, I'll have a go at that over the weekend. I have already ordered some different tubes, just to see how they affect the sound as this is the first tube amp I have owned. They won't arrive for a few weeks tho, so I'll test with the chopstick method first.

[watonwak]

So after reflowing the ground path I did a resistance check I am now getting 2.4K on terminals 6 and 10. the rest are normal. Any idea what i have done?

[Paul Birkeland]

Can you post some photos of your build?  Specifically I'd want to see the wiring around the headphone jack and 8 pin socket.

-PB

[watonwak]

are these okay?

[Paul Birkeland]

I would bet that if you took your needlenose pliers and pulled on each of the black wires where they attach to the headphone jack, one is probably loose and not captured by the solder joint.  That is why you see 2.4K at 6 and 10 instead of 0.

[watonwak]

They are both well attached, but I reflowed the joint anyway. I'm am still reading 2.4k

[Paul Birkeland]

Do you have an 1/8" to 1/4" adapter plugged into your headphone jack by chance while you've been taking these measurements?

[watonwak]

Yes! that was the problem!

All the measurements are now good!

I also cleaned the pins on both tubes with some iso and the noise seems to have gone!

Hopefully no more drama until I attempt the speedball upgrade

Thanks for your help!

[kill_surf_city]

Yes! that was the problem!

All the measurements are now good!

I also cleaned the pins on both tubes with some iso and the noise seems to have gone!

Hopefully no more drama until I attempt the speedball upgrade

Thanks for your help!

What did you use to clean the pins? I'm having the exact same problem you had.

[Laudanum]

You can use some 0000 steel wool to clean the tube pins.  Shines them right up.  Just do it away from the amp (you don't want steel fragments and dust falling into the amp.  If you have NOS or UOS tubes, just be careful in handling the tubes if you care about the labeling on the glass.