random crakling sound on Fender red knob twin

[jalexquijano]

The crackle on my 1990 Fender Red Knob Twin came back yesterday. It is just random, meaning it appears suddenly and then its gone. Should i also tighten and clean the tube sockets again?

[g1]

Try wiggling them around in their sockets and see if that causes the crackle.
Could be a tube too.

[jalexquijano]

Ill check on that! I guess ill need to replace all those 12ax7 fender tubes. I thought it was only V7 that caused that random crackle.

[Enzo]

Just about every part in the amp goes into making sound, and by extension, just about every part can cause noise. Don't tell yourself that only one part can make a noise.

Ball up your fist and whack the amp hard. Does that cause a crackle? Does it make a crackling stop?

Crackles CAN be caused by tubes and/or tube sockets. But also resistors ar often causes of such noises. Solder connections are prime suspects.

Something as simple as a loose nut on a control or a jack can cause such noise. In fact, even a snug nut with a star washer underneath that has oxidized can.

[jalexquijano]

Just about every part in the amp goes into making sound, and by extension, just about every part can cause noise. Don't tell yourself that only one part can make a noise.

Ball up your fist and whack the amp hard. Does that cause a crackle? Does it make a crackling stop?

Crackles CAN be caused by tubes and/or tube sockets. But also resistors ar often causes of such noises. Solder connections are prime suspects.

Something as simple as a loose nut on a control or a jack can cause such noise. In fact, even a snug nut with a star washer underneath that has oxidized can.

I tightened and clean the sockets with DEOXIT D5. no more crackling although hum in the background is still present.

[jalexquijano]

Just about every part in the amp goes into making sound, and by extension, just about every part can cause noise. Don't tell yourself that only one part can make a noise.

Ball up your fist and whack the amp hard. Does that cause a crackle? Does it make a crackling stop?

Crackles CAN be caused by tubes and/or tube sockets. But also resistors ar often causes of such noises. Solder connections are prime suspects.

Something as simple as a loose nut on a control or a jack can cause such noise. In fact, even a snug nut with a star washer underneath that has oxidized can.

i have already tightned and clean all the power and preamp tube sockets, changed the 470k grid resistor but still experimenting some random crackle every once and then. Today i Heard it after 45 minutes of playing. WHich other resistors could be suspect?

[nevetslab]

Good chance it's one or more solder joints on the control panel PCB. On that amp, getting that board off is tedious, but, you're looking at the solder side of the board. Take a close look with bright light and magnification and take your time going over the entire board. Using an insulated tool, like the back end of a screwdriver where you can tap on the board with the volume up just enough to hear residual noise and controls as you rack them back and forth, it can help reveal the cuplrit(s) I've found volume controls and tone controls causing this crackling. Sometimes its controls needing cleaning, sometimes it needs them being replaced. No absolutes in trying to find the cause. As Enzo said, could be most any component. And, always with enough gain following it to make itself known. Welcome to the tedious end domain of spot the looney.

[jalexquijano]

Thank you very much. I will check those solder connections

[mikeydee77]

Are you able to check voltages safely?

Might be worth seeing if there is any DC voltage leaking from the tone stack caps.

Usually middle pin of treble pot is often a good place to check. You should find 0v DC but if a cap is leaking, then you may get a few volts which will give excessive crackling...

[jalexquijano]

At the moment, i have only done the following to the red knob twin "THE TWIN":

1. Tightened power and preamp tube sockets

2. Spray DEOXIT D5 to all sockets

3. Replaced the input stereo Jack which is most used when i plug the guitar. All of the other jacks have been left untouched.

4. Swapped V7 and V1 with non microphonic 12ax7 tubes.

The amp sounds fine. However after minutes of playing you can hear this crackling which sounds as an old vynil record with or without the guitar being plugged to the amp. Should i consider replacing the preamp and power tube sockets also? All the electrolytic caps were replaced 3 months ago.

[nevetslab]

You can try swapping them out. I'll often remove the 12AX7 in the Tremolo circuit to see if it's quiet enough for use in the gain stages. Every once in a long while, I'll get a power tube that's emitting a random snit. You could operate for testing purposes with only one pair of output tubes installed, just to see if the crackling stops. Then, swap the installed pair with the pair you removed..

I had to track down the microphonic source on a Vox AC30-CC2X this past week, had no spare EL-84 tubes on hand (and didn't feel like going and fetching another AC30 to take apart and rob it of its' tubes), so it was all done by substitution, and finally found the offenders.

[jalexquijano]

You can try swapping them out. I'll often remove the 12AX7 in the Tremolo circuit to see if it's quiet enough for use in the gain stages. Every once in a long while, I'll get a power tube that's emitting a random snit. You could operate for testing purposes with only one pair of output tubes installed, just to see if the crackling stops. Then, swap the installed pair with the pair you removed..

I had to track down the microphonic source on a Vox AC30-CC2X this past week, had no spare EL-84 tubes on hand (and didn't feel like going and fetching another AC30 to take apart and rob it of its' tubes), so it was all done by substitution, and finally found the offenders.

My power tubes are Brand new and matched. So this must part must be ruled out. Ill check on the preamp tubes starting from v7

[Jquijano]

Hi guys its 2022 and im still having this frying bacon sound produced now more continuously in my 1990 Red Knob Twin. This happens with or without the guitar cable plugged. Any resistors I should replace and which ones? I cannot go to a gig with this amp like this.

[Helmholtz]

Might be a plate resistor.
Please post schematic.

[Jquijano]

Might be a plate resistor.
Please post schematic.

Please find attach list part and schematic. I have the amp on and will open it once I start hearing the frying bacon noise. i can troubleshoot this with a wooden pencil or stick respecting the dangers of high voltages in this amp. Can you point out which plate resistor shall I be looking at?