Inside the amp (high voltages etc) a shard of thick aluminium foil. Does anyone fully strip off the screening foil on the insides of the cab, both ends of the amp, and spray with "Tempest" proofing nickel RF/EMI spray. Or as valve stuff anyway, just remove those sheets of aluminium foil and how much extra noticeable hum? Was it just to save the cost of closing the chassis, at both ends, with expensive full thickness steel?
** The modern Fender "Deluxe" comes in two version, Hot Rod and Blues. Fender made amps in the 50s and 60s simply called Deluxe, but these were quite different to the above. The full name is printed on a metal plaque on the back panel.
HR and Blues Deluxes are quite cheaply made, but have no serious flaws aside from having fragile plastic input jacks. The chassis is folded from one piece of steel sheet with the control surface nickel plated and screen printed. Additional static screening is provided by self adhesive foil applied at the ends and on the detachable back panel.
Most valve guitar amps have a fully screened chassis, often with aluminium sheet or wire mesh attached to timber surfaces to complete the job.
If this screening is missing of left out, the amp will make buzzing noise when the volume is turned up - particularly if the room has any fluoro tubes or dimmers. Shops with valve amps on display and demo typically have fluoro lighting, so this can be an issue affecting sales.
Lack of full shielding can also result in high frequency oscillation at high volume and tone settings - due to close proximity of speakers or guitars with poor shielding of the pickups and wiring. Some combo amp makers routinely ground the speaker frames for this reason.
Supersonic oscillation can seriously damage a valve (or transistor) amp so must be avoided.
... Phil
Hot air and the remnants of that foil soon came off. Masked off the edges and sprayed the nickel spray on the cabinet sides. When wet , the point contact across a diagonal , 6 or 8 inches, >30M, 20K after 1hr, 90R after 3 hr, 30R after 6hr. So hopefully by tomorrow and distributed ground contact along 3 edges will be sufficient. For safety reasons that foil had to go. I suppose the proper way round this notorious problem is, strip of the foil, depth stopped fly cuttter, router, end mill or whatever and then full thickness metal sheet set in the recess.
down to 15R after 20 hours
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