Vintage Kenwood Amp Mains Wiring

[reddish75]

I'm repairing a Kenwood Model 500 amplifier finally after buying it 5 years ago, part of that sale was to take the aftermarket 'audiophile mains cable off' for the seller, however now I've come to put a new one in I'm not sure its wired correctly?

Neutral is fused not live, not sure this is the way it was from factory? Should this be changed? Please see rough drawn diagram of how it was and the factory schematic, I'm assuming its the UMX type as its the only one with a 4 amp fuse.

[Nickthedentist]

Is it double insulated, or was it meant to have an protective earth wire in the mains lead originally? It was quite common for the UK models (usually branded Trio) to have an earth wire, and the overseas models (Kenwood) to have none.

What is the suffix after the model number on the actual unit you have in front of you?

I don't like the idea of a 40 year-old suppression cap strung directly across the mains, before the switch and fuse.

If it were mine, for my own personal use, I think I'd rewire it for 240V only operation (i.e. disconnect the selector and wire the primaries in parallel), have the fuse in the L line, and use the DP switch to break L and N, finally snipping out the cap. But if it's for someone else, that would be opening a whole can of worms.

Nick.

[GrimJosef]

I guess you mean "... wire the primaries in series ..." Nick.

Cheers,

GJ

[Nickthedentist]

Er. good point, GJ

[reddish75]

Originally Posted by Nickthedentist

Is it double insulated, or was it meant to have an protective earth wire in the mains lead originally? It was quite common for the UK models (usually branded Trio) to have an earth wire, and the overseas models (Kenwood) to have none.

What is the suffix after the model number on the actual unit you have in front of you?

I don't like the idea of a 40 year-old suppression cap strung directly across the mains, before the switch and fuse.

If it were mine, for my own personal use, I think I'd rewire it for 240V only operation (i.e. disconnect the selector and wire the primaries in parallel), have the fuse in the L line, and use the DP switch to break L and N, finally snipping out the cap. But if it's for someone else, that would be opening a whole can of worms.

Nick.

It will have been a two core mains wire from factory so double insulated, it's a multivoltage probably international model. Suffix is E.P but is identical to the U,M,X type

A new mains safety cap will be installed.

My Dad is going to have this so needs to be safe. I don't mind rewiring this but wondering if this how it was originally is it best to leave it as is. Also what are you referring to 'opening a can of worms'?

[Nickthedentist]

I just meant from a legal point of view.

If it's for a loved one, just do what's best from a technical point of view.

I would probably fit a 3-core lead if it were mine, bearing in mind the possibility of hum loops if the other components have 3-cores.

[reddish75]

Originally Posted by Nickthedentist

If it's for a loved one, just do what's best from a technical point of view.

I would probably fit a 3-core lead if it were mine, bearing in mind the possibility of hum loops if the other components have 3-cores.

So if this was yours it would be wired for 240v operation, with a 3 core lead, bringing live and neutral to the switch then transformer?

[reddish75]

Or could it be done like this, with a protective ground?

[cmjones01]

It looks like it had a 2-core mains lead from new, as most hi-fi equipment does. If so, it was probably built as double insulated, or whatever the nearest acceptable standard to that was at the time. There will be no benefit to adding a protective earth as long as your wiring mods maintain the double insulated construction: make sure that all potentially live wires have at least 2 layers of insulation between them and anything someone could touch. One layer of insulation can be an air gap. That's why there's often a plastic shroud over mains switches with exposed tags, or a plastic shield under PCBs carrying mains voltages.

Bear in mind that in a 2-wire appliance like this there's no such thing as live and neutral. In most of the world the mains plug can be inserted either way round, so you have to consider both wires as being live (indeed, in some places like Belgium and Norway both wires may very well be live at the same time - 220V mains is to be found between two 127V phases). It therefore doesn't matter at all which wire the fuse is in.

Chris

[Richardgr]

Just looked at HiFi Engine ...
Kenwood model 500
Looks very tasty!