Vox Ac30CC2 "ghost" sound

[rockaffe]

I would like to ask for some advice about the annoying noise that occurs when I use distorted pedals on a vox ac30 cc2, mostly to understand if it is a problem with the pedals or the amplifier.
This noise (which sounds more like the same note played twice than a noise) is not particularly loud in volume, but it is still very annoying to me as a player.
In some articles found online I read that it could depend on coupling caps but I would like to have some advice from those who understand them more than me.
This amp has been off for almost 10 years and in the last year I have replaced the rectifier valve, power tubes and filter capacitors, as well as a general cleaning of all contacts.
In case you advise me to replace the coupling caps, I would like to ask you, since here in Italy I cannot find the Mallories, if the Vishays can be a valid alternative.
Thanks so much.

[Jon Snell]

Any decent polyester capacitor of the original value and voltage ratings will be fine.
This has a PCB so you will be limited to space for fitting them, not that replacing them will improve anything.
If a coupling capacitor is faulty, it is usually leaky.
I would not use a distortion pedal, it is a VOX not a Marshall.

[Chuck H]

John is right that dirt boxes aren't typical with the AC30. At least not in popular forums. But...

As it happens there are a great many recordings spanning many years for the Foo Fighters that use AC30's and dirt boxes. But I digress.

The usual MO with AC30's is a boost pedal. Well... Dirt box, boost pedal,... Which one seems more likely to throw an amp into ghost notes? Not that it's necessarily the problem your having, but it sounds like it might be.

It might help to know what volume you're playing at with the dirt boxes in the signal chain. Are you using them with boosted output and cranking the amp? Are you running the amp fairly low in volume and using the dirt boxes for low volume distortion?

There's also a small possibility of something called "cone cry". Some flawed speakers, when pushed with square waves, can exhibit sum/difference notes because of their skewed resonances. Plugging the amp into an extension cabinet, bypassing the normal speakers would reveal this easily.

[Helmholtz]

Many players (including Brian May and myself ) use(d) an AC30 with a treble booster.

Ghost notes are more likely with a strong bass content in the signal. So a treble booster helps to avoid that effect.
Apart from that I never really had that kind of problem e.g. with a Tubescreamer into the AC30.

As ghost notes are typically caused by signal intermodulation with amp ripple/hum, I would check the amp for that first.