Grounding a vintage Fisher 400?
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Wodgy

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I'm a vintage gear newbie, and I'm wondering how/if I should ground a Fisher 400. The stock power cable just has two pins (no ground), and the only other piece of gear I have (a CD player) isn't grounded either. It sounds great, no hum or anything, but I'm concerned that when I'm listening with headphones my body would end up acting as a ground if a short happens. Especially with Etymotics.

Does the Fisher 400 use its chassis as a simulated ground? Can I properly ground the amp just by attaching an alligator clamp to the chassis and connecting a wire to the ground of a power outlet? Or is there a better way to ground it?
 
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mkmelt

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I don't think the Fisher 400 receiver needs to be grounded, as the design uses a floating ground. The Owner's Manual states that if you get audible hum, through the phono preamp or other inputs, then you should reverse the plug in the wall receptacle or power strip. This will usually reduce the hum.

There is nothing in the manual about connecting the ground wire from your turntable to the chassis of the Fisher. While there is no labeled grounding post on the chassis, I believe you can attach the turntable ground wire to one of the side or rear chassis screws if you find you are getting a hum without attaching this wire to a ground. But just to be sure, I suggest you ask Tuberoller, as he has alot of experience with the vintage Fisher gear, including the 400 receiver about issues associated with grounding this type of equipment.

It is however, important to make sure that the receiver has been properly maintained over the years. Most importantly, that means replacing the aging selenium bridge rectifier (usually a 2 inch square widget labeled Siemens mounted to the rear right side panel of the chassis) with a modern solid state rectifier.

Another simple but effective safety mod involves soldering a set of four resistors into the power tube circuitry to act as fuses in the event of one of the 7868 power tubes shorting internally. Much better to pop a 50 cent resistor than to watch the whole chassis, transformers and all, go up in smoke.

If you are really worried about getting a shocked or cooked through the headphone output, I suppose you could wire a fuse into your headphone cable.

One of the things I like about equipment of this vintage is that manufacturers could assume a certain level of knowledge and common sense on the part of the consumer. No need for a warning label on the chassis of the dangers of the high voltages lurking inside. Somehow people knew that the insides of radios, stereos, and televisions were not something to start poking your fingers into unless you wanted to get a nasty shock or worse.

Fortunately, a Fisher 400 receiver is too large and heavy to encourage much placement experimentation. This is one amp that is definitely not for listening poolside through headphones, or while relaxing in a bath tub.
 
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Tuberoller

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Tuberoller the Journeyman Electrician will once again advise anyone who will listen to use an Earth Ground.This will eliminate all grounding problems.Most of the grounded outlets you see,especially in residential use,are grounded only to the structure of the house,or worse yet, only to the outlet box if there is a box.In most industrial applications there is a seperate ground,usually a green wire,that is actually grounded at a junction or circuit box.The best type of ground,an earth ground,is actually, as the term implies,grounded to the earth.I was forced to use an earth ground due to massive RFI from a radio tower located less than half a mile from my house.I found other benefits of doing this like much lower noise floors in all my audio gear and clearer pictures in my video gear.I knocked an iron pipe six feet into the ground right next to my house and ran wires straight to my main circuit box.I ran another right to my listening room and the circuit box that I use there.This ground wire is run through every outlet in the house and a redundant ground is used in the listening room.All the racks are grounded to the earth ground as well.One warning I will issue when using an earth ground:use a surge protector.If the ground is somehow lost ,surges will run rampant.On the other hand,you are much less likely to suffer power surges due to the earth ground.Another benefit of an earth ground is that any line conditioning that can be added to one circuit can effectively be added to the entire house.What I mean is,if you have something like a high current line conditioner you can add that conditioner to the circuits of the entire house before the fuse/circuit box if the box is grounded before the circuits.I don't do much residential work anymore but this is how we add surge protection to the entire electrical systems of buildings like hospitals and schools.

The Fisher does indeed have a "floating" ground but that term is deceptive in this use.The chassis of the Fisher is not truly grounded.When used to ground phono leads hum can be introduced if the chassis is placed on a surface with a poor ground or a conductive surface.In simple terms the circuit of the Fisher relies on the chassis being placed on a non-conductive,grounded surface(such as the original cabinets)to complete the ground.You can easily ground the chassis if you have a concern about electrical shock or ground induced hum.If you need a copy of the schematic of a Fisher 400,500 or 800 I can send you one with an addition that shows how the chassis should be grounded.Insurance is never a bad thing.
 
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Wodgy

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Thanks so much for the detailed responses!
 
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