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?

N_Cook wrote:


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

On 17/11/2015 16:03, N_Cook wrote:
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?

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