Intermittent crackling noises in a new AC30 TB w or w/o a guitar connected

[archaos]

Hi there,

             I've just finished another AC30 TB (w/o VIB/TREM channel) built from scratch, & it emits sometimes some crackling sounds.
             The plate res. used on V1 are 220K 1/2W Allen Bradley carbon comp, but they read 250K. Do they resist too much ?

            

            

            

             

             Can those noises be produced by stg else ?

               Thanx a lot.

[Dave]

"Can those noises be from something else?"

Yeah, check the tubes and tension the sockets first.

Dave

[Tiny_Daddy]

Check if you forgot to solder something. Also, tap around with a chopstick or plastic screwdriver handle.

[archaos]

Thanx guys, I'll do my homework.

[archaos]

Homework done, nothing seems suspect ; it can crackles w/o playing the guitar too, therefore I guess it is an electrical issue...Any idea ?

[archaos]

I'm back. Perhaps stg new : when poking either the PIN2 1M grid res. of V3 (phase inverter) or the PIN2 itself it crackles ; nothing happens elsewhere.
So, is due to a bad resistor, a bad solder joint, or something else ?

[RicharD]

Check the solder joint itself first.  Go ahead and reflow it.  Sometimes even good looking joints can be cold and cause crackling.  Sometimes a bad resistor can cause crackling, but usually it's a plate resistor sitting at a high potential and flowing current.  A 1M grid resistor is neither sitting at a high potential nor flowing current.  It could easily be bad tension at the socket too.

[archaos]

Thanx a lot, I'll try & report it. 

[sluckey]

when poking either the PIN2 1M grid res. of V3 (phase inverter) or the PIN2 itself it crackles

That crackle may indicate a problem but it is also quite normal to poke the high impedance grid of a LTP PI and get a static crackle sound.

[jojokeo]

Ditto on touching up solder joints. Building fast and flowing solder relying on it's internal paste for new & shiny (or worse, dirty) metal can cause bonding issues. Kind of like gluing PVC pipe w/out solvent to prepare the weld as there's an unseen slippery grease film left from the extrusion process. You properly prepare pipe and fitting before gluing. In soldering you pre-tin both components before soldering but we rarely do this when the build "is on". I don't mean this to sound like soldering 101 or demeaning becuase you obvously know what you're doing to build amps like that. But for others learning, this could hopefully help them in understanding?
Keo

[archaos]

Have swapped all the tubes with my other AC30, checked the socket tension, re-soldered PIN2, & swapped the suspect 1M res. Crackling is still there...What's next ?

[Tiny_Daddy]

Pull tubes, starting with the first preamp tube. Find the minimum tubes that still crackle.

[archaos]

Excellent ! Thanx, will check...

[J Rindt]

As soon as I read "carbon comp", I think Noise. I am surprised they get used anymore. You may have burned up a plate resistor when you soldered, or it might just be noisy all on its own. If you can pull pre tubes and find out where the crackle is coming from, try replacing those plate resistors, try carbon film or better; unless you are worried about the components that were shelf items 40 years ago
You can always put the CC's back in......
Good Luck

[archaos]

Pull tubes, starting with the first preamp tube. Find the minimum tubes that still crackle.

V1 pulled, crackle's gone.  What do you suggest ?

Good Luck

Thanx.

[Tiny_Daddy]

Disconnect the plate resistor on each section (pins 1 and 6) and see which one makes it stop.

[archaos]

Disconnect the plate resistor on each section (pins 1 and 6) and see which one makes it stop.

Sure I will, thanks !

[archaos]

Have removed the PIN 1 plate res.&  crackle is still there, I hope that's the other one connected to PIN 6. Will report this evening...

[archaos]

A last test on PIN 6 has finally proved its plate res. was faulty.
Tiny-Daddy I owe you beers  thanks again !

I must admit too, thanks to this goldmine forum I had solved a standby fuse blow due to a gassy rectifier.



Thanks guys.