The AM Forum

... hi from tim...i've been thinking about rewiring my old gear...i want to convert these old rigs, and go with 3 prong grounded plugs...ok, some of the old gear has the old 2 fuse plugs, which blow if something is going wrong.. what are your suggestions for converting to 3 prong plugs?...especially some of these ones i'm now seeing that have a polarized side?...fusing, the gnd pin to the chassis, etc...sk...

only fuse the black hot, neutral and safety ground do not fuse

Frank said:
Absolutely!!! I used to replace those "double-fused" plugs because of retaining the original looks of the rig. Then I realized what could happen. Since then, I have begun a program to replace the two-prong with three-prong. Making sure the fuse is in the hot leg. Also, I generally replace the cord with with one that is more 'hardier' than the original.

As already stated

The black lead is "hot"... and it should be connected to the narrower of the two flat prongs on the plug (assuming the wall outlet is wired properly). At the rig, the black lead should connect to the fuse... and the other side of the fuse should connect to the "on-off" switch. The output of the "on-off" switch should connect to one side of the primary of the transformer.

The white lead is "neutral", and it should connect to the wider of the two flat prongs on the plug. At the rig, the white lead should connect directly to the other side of the primary of the transformer (no fuse, no switch).

The green lead is "safety ground". At the plug, it connects to the non-flat prong. At the rig, it should be connected directly to the chassis of the rig.

If the rig doesn't have a power transformer (e.g., some older receivers), then you should consider adding a small isolation transformer to enhance its safety. You don't want to use a 3-prong cord/plug if the rig doesn't have a transformer... because you don't want to directly connect the "neutral" and "safety ground" leads at the rig. Doing so can mess up the functioning of ground fault interrupters... and possibly cause other functional and safety problems.

Even if you don't convert to a 3-prong plug/cord...if you ground the chassis of a rig that doesn't have a power transformer: when you plug it in, you will either blow the circuit breaker because you have connected the "hot" power lead to ground... or you will cause the "neutral" power lead to become connected to ground (at a place where it shouldn't be connected to ground). If you don't ground the chassis... then you have a safety hazard. Therefore, it is a good idea to add an isolation transformer to any transformer-less rig you plan to use.

Some rigs, like the Johnson Ranger, employed two (2) fuses: e.g., a 3 amp slow blow fuse, and a 5 amp fast blow fuse. If you want to keep both fuses, put them in series (attached to the black lead). Do not put either fuse on the white/neutral lead.

Doing the above will ensure that the black/hot lead will be opened when either fuse blows, or when the on-off switch is in the off position.

Best regards
Stu

Oxygen free 12 ga. that's been "burned in" is the cat's PJs !!!!
And remember to use the gold plated fuses for better frequency response.

See it here (http://www.coolgales.com/store/cart.php?target=product&product_id=304&category_id=55)

Ah yesss,

Yeh gots ta love them audiophools!

73,
Ellen - AF9J