amp cracklin

[fopoman]

gettin some weird cracklin sounds from my latest build. tubes are fine. Turn the voume all the way down and you still hear it.

thanks,
nathan

[tubeswell]

Quite possibly bad tube or bad soldering (or maybe a leaky board?). I had this on a new build last year - turned out to be a bad presence pot where the flux or solder had somehow run into the pot causing voltage leak. A new pot fixed it. Not saying that this is your problem tho'.

[fopoman]

cool. tried removing just the phase inverter tube. cracklin stopped. any more ideas?

[rfgordon]

fopoman,

Did you try pulling the other preamp tubes in turn first? If not, do that. If so, then the noise is likely in the PI. Try a tube swap first, then reflow the joints on the plate resistors.

If that doesn't fix it, tap the plate resistors with a chopstick. If one of them crackles, replace it.

[tubeswell]

Okay that's freaky - was similar symptoms to my problem. Does clipping your V meter on the grid side of the PI input coupling cap stop the noise? Has your PI got a presence pot?

[Structo]

Yes it is no wonder that when you pull the PI tube there is no sound since everything has to flow through that tube to get to the power tubes.

In the order of suspicion:

1) tubes (take a known good preamp tube and substitute it one by one with the tubes in the amp)

2) Power tubes (same deal, try different ones and don't forget to check the bias).

Chopstick components, start at PI and work towards V1.

Not all things are equally likely to fail. Experience with tube guitar amps has shown that failures are most often in the following order of likelihood:
1. Operator Error - a control or something is set or switched wrong.
2. Tubes - the most likely thing to have gone bad on a once-working amp; this is why they're in sockets!
3. Power Supply Components - they handle lots of power and get hot
4. Resistors and Capacitors - especially electrolytic capacitors
5. Mechanical Components
o Tube Sockets
o Switches
o Switches
o Cables, Cords and Jacks
6. Internal Wiring
Accordingly, suspect problems in that order. First make sure you are operating the amp correctly - master volume turned up, cords plugged in, etc, etc. Then suspect that a tube has failed, and so on.

Taken from Geofex.com written by R.G. Keen

http://www.geofex.com/ampdbug/ampdebug.htm

[fopoman]

cracklin is still there when i pull the first preamp tube.

[Andy Le Blanc]

I'm thinking a resistor too, It ok to pull the PI tube, no noise tells you its not in the power side.

Bad wire, bad join, bad resistor, intermittent resistors can be tuff.

Get in there with the power off, unit unplugged and the caps drained and.....
put a little kink in the resistor leads, the slight tension can fix or reveal the fault.

[fopoman]

thanks...i give it a try

[Gaz]

I've had this problem before, and in my case it was also a 'bad' pot. It wasn't sealed, so I'm sure something just got in there. Cleaning didn't help, only replacing it.

FWIW, I know bad plate resistors tend to cause the crackles too, but I've only found that on an older Fender.