I can hear a rustling sound from the 'speakers

[FAQ Team]

This is usually caused by poor valve/base contacts in the first or second stages, or possibly a noisy valve.

Bad contacts can be cured by cleaning both the valve pins and base with a proprietary cleaning solution* and stiff brush, and then GENTLY tightening the base sockets**, with the amplifier turned off of course.

Noisy valves, either electronic or mechanical noise can really only be cured by replacement.

*Proprietary cleaning solutions, available from RS, Farnell, Maplin, local chemists, DIY stores etc.:

The most common is IPA = Isopropyl Alcohol = Isopropanol , sometimes called Computer Cleaner, Electronic Cleaning Solvent. Be aware that some of these items will affect plastics and the like, so use carefully and in well ventilated areas.

It is also useful to have a pressurised aerosol duster to blow surplus IPA away quickly and easily.

When the item is clean, you can if you wish, use a contact lubricant such as Electrolube or any one of the advertised gold type treatments. RS/Farnell/Maplin do an excellent range of lubricants in small pen-type containers for precision application. DO NOT overdo the lubricant, too much is worse than too little. Be aware that although these lubricants are conductive, some are extremely conductive.

**To tighten valve holders needs some care but can be done with a pointed tool such as a metal workers scribe. REPLACE the scribe between the valve base insulating material and the pin and GENTLY force the two (usually) parts of the pin together by equal amounts. Don’t overdo it, as you will then not be able to put the valve back in, defeating the object of the exercise.

Providing that you are not an ardent valve swapper (and most of us are) you may not have to do this at all