Crackling in '74 Twin Reverb

[Paul Marossy]

I don't play my Twin much these days, but I have noticed that I have a little bit of a crackling noise when I pull the master volume boost out. Does anyone know what the cause of this may be?

[cbarrow7625]

Dirty switch contacts and/or dirty pot.

The quick & easy way to try to alleviate the problem is to push & pull the switch in & out rapidly a bunch of times, that will sometimes clean the contacts if it is only a little bit 'o grime.

Try the same thing with the volume pot. With the amp OFF, turn the volume knob back & forth from 0-10 rapidly a bunch of times. With a volume pot this almost always works. Since the wiper makes contact with the surface, it just "snow plows" its way through the grime.

I would do that to every pot on the amp if you don't play it often. The inactivity is the cause. If you check inside the pots you'll find amp tears.......

[Paul Marossy]

Cool, thanks for the tip. I'll give that a try.

[pdf64]

Do you get the same (but reverbified) crackling if you turn the reverb up full? I'm thinking that the reverb driver v3 is very stressed in silverface amps, so it could be that tube or it's associated components on the way out - Peter

[Paul Marossy]

Do you get the same (but reverbified) crackling if you turn the reverb up full? I'm thinking that the reverb driver v3 is very stressed in silverface amps, so it could be that tube or it's associated components on the way out - Peter

Not sure. I'll have to check for that.

[pdf64]

What I should have mentioned is that the pull boost feature uses the reverb drive signal.
But theproblem might also be v2 going noisy, or v2 plate resistors, or the pots as suggested above - Peter

[tommy d]

If you check inside the pots you'll find amp tears.......

Very Funny!

[Luthin You]

the old fenders often suffer conductive eyelet board , sometimes if you remove the screws that hold down the board, then pry the upper board away from the lower one, the noises stop.Use lots of caution here , Im a tech and you're probly not.If this works just insulate the upper board by shoving some rubber or plastic under the noisy area.Then tighten the screws a little>

[tommy d]

Mine 1968 twin had the same problem on only the reverb channel. After reading this post I ordered some A/B 100k and replaced the two 12AX7 plate resistors and the problem went away. It was like magic and cost $2.00.

My twin sounds awesome, thanks for the knowledge.

[EffectsGuru]

I would try using some DETOX-IT (its an electrical contact cleaner), luthiers use it all the time for the pots on your guitar, so that won't hurt your amps pots but MAKE SURE YOUR AMP IS OFF and MAKE SURE ITS DRY before turning back on. You need only spray it at center post and let it run into the contact inside... than turn the knob back and forth... that should alleviate the issue if it is in fact from dirt.

[R.G.]

The plate resistors on old Fender amps are practically notorious for making crackling sounds. This has been in the Tube Amp FAQ since it's first release, pre-dating the advent of the web, back from the days of the usenet.

It's still at geofex.com for archival purposes.

Crackling is always caused by discontinuous flow; that means an aging carbon comp resistor, crystalized solder joint, DC on a pot, dirty switch or tube socket contacts, or a cracked/broken component or lead.