Lightning build-Static, crackling upon power up

[theundeadelvis]

So a while back I built a Matchless Lightning clone with the ability to use 6V6 or EL84 tubes. It worked fine for a while, but then it developed an intermittent problem when you switch it on or off.

This happens sometimes but not every time when you turn the power on:
You flip the switch to on it takes maybe 30-40 seconds to warm up. As it gets to the the end of that 30-40 second warm-up you can hear static and crackling coming through the speaker that gradually increases in volume. Then as it reaches a point where everything is warmed up the sounds quit and the amp works fine. It makes no weird noises when you play it either.

Sometimes when you turn it off you get the reverse effect. Flip the switch off, instant loud static and crackle that fades and disappears.

I replaced all the preamp and power tubes (haven't tried a different rectifier yet), rewired the inputs, reflowed a few solder joints, and chopsticked. No luck. I'm about ready to start rewiring everything and replacing all the caps because i am at a loss.

I will be forever grateful for any advice anyone can offer! Thanks in advance.

[theundeadelvis]

The layout I'm using is at the bottom of the attached PDF. One thing I noticed, that I'm not sure if it matters, is that on this layout the 3 watt 100 ohm resistors going to the power tubes screen grids is connected to the 33uf filter cap and on other layouts (like Ceriatone's) they go to a 22uf (which the layout I used doesn't even have)? Could this be a problem?

[theundeadelvis]

I replaced both input jacks (one was not switching properly), and so far it seems to have fixed it. I'll keep my fingers crossed.

[Bob-I]

IME this is usually caused by a cold solder joint. I just fixed one yesterday with the same symptoms. I poked and prodded with a chopstick until I found an area where the crackling changed as I prodded. I then focused on the solder joints and found one that when tapped, the crackling stopped, until the next power up.

I Reflowed the joint, no more crackling.

My guess is that you had a poor contact on the jack OR a cold solder joint.

[theundeadelvis]

Yeah, I think it was the contact of the switch in the jack. I never noticed it with a cord plugged in, and it crackled bad if I barely touched the jack tip contact. The only thing I find weird is why it only happened when the amp warmed up and not all the time? It still seems fixed, so I am happy. Thanks!

[Structo]

Probably from the expansion/ contraction of the heat.
Many things are heat related for this reason.

[Rick]

I would guess about 95% of problems with new amp builds are input jack related and/or bad solder joints somewhere. The joint can even look OK, but if a wire is just pushed into a tab and soldered without tying or wrapping or crimping it somehow, it can look soldered but it will soon turn or spin in the joint and make poor or no contact. This can drive you nuts trying to find it at first.

I always make a mechanical connection so the solder grips the wire in a more complex way than just a stab straight through the tab. That keeps the wire from breaking free and spinning in the joint and generally prevents this type of problem entirely. Good luck with the amp!

[HeeBGB]

The screen feeds on the Ceriatone AND Trinity layouts are incorrect. I built it the way their layouts are and the screen voltage was 140Volts. WAY too low. I fed the screens from the other side of that 22k resistor (the choke side) and the screens were about 350V. The amp was much better sounding BUT it will eat tubes very quickly. I added a 1.5k resistor to bring it down a little but from what I understand from a few friends that have had real lightnings on their bench.....the screens run VERY high!

This doesn't really help with your problem BUT when you get it sorted out you should take a voltage chart and if your screens are low you know why!