Cap wiring question

[tribi9]

I scored a couple of NOS can capacitors that im going to try to reform with the help of a Variac.

The question is tho, the old caps have a negative and positive tab. The way they're wired tho', one of doesn't have a chassis ground reference while the other one does.

If I use of those spacers you see on the last pic to isolate the can to the chassis. would I be able to use the unmarked tab in the can as the negative?



[IMG:800:600]http://i114.photobucket.com/albums/n271 ... 171317.jpg[/img]

[IMG:800:600]http://i114.photobucket.com/albums/n271 ... 171301.jpg[/img]

[IMG:800:600]http://i114.photobucket.com/albums/n271 ... 194546.jpg[/img]

[tribi9]

FYI...

The new cans im using now tho, all are metal with 3 sections. Im using 2 in parallel to get me 100 mfd. 3 tabs are marked and there's an extra tab with no markings. (Plus 4 mini tabs to attach to the chassis.

The old cap has has 2 tabs only, one negative and one positive.

Sorry for the dumb question, but im just a little confused here...

[epis]

Hi,
old can caps have minus marked with black paint, multicap cans have pluses marked with triangle, square or circle, minus is common and unmarked.
You MUST connect minus to minus or plus to plus, other way cap can explode.Good luck, best regards from Ottawa.

[tribi9]

Thx for the reply! So i can isolate the can from the chassis with the spacer and use the unmarked tab on the multisection then and I should be ok?

[Firestorm]

On Type FP caps (like the NOS ones you have), the negative terminal, the four mounting tabs and the can itself are all negative, so insulating the can may involve more than just the insulating spacer. It looks like the old caps are wired in series, which means that half of the B+ voltage will be on the can of the first series cap. When used that way, FP caps used to have thick cardboard insulator sleeves to keep someone from reaching into the back of the amp and frying himself on the exposed metal.

So you need to make sure the mounting taps aren't too close to the edges of the chassis hole (may need to enlarge it) and you need to insulate the can of any cap where the negative is not grounded. There is some large heat shrink used by electricians. It might be big enough.

[tribi9]

On Type FP caps (like the NOS ones you have), the negative terminal, the four mounting tabs and the can itself are all negative, so insulating the can may involve more than just the insulating spacer. It looks like the old caps are wired in series, which means that half of the B+ voltage will be on the can of the first series cap. When used that way, FP caps used to have thick cardboard insulator sleeves to keep someone from reaching into the back of the amp and frying himself on the exposed metal.

So you need to make sure the mounting taps aren't too close to the edges of the chassis hole (may need to enlarge it) and you need to insulate the can of any cap where the negative is not grounded. There is some large heat shrink used by electricians. It might be big enough.

So if I use the insulator I guess, ill be isolating the cap from the chassis yet the can will still be live. Shitty...

[tribi9]

Thank you all, it all makes sense. Simple enough, I just for some reason didn't think you could wire capacitors in series and that helped with the confusion. I'm going to buy some heat shrink and wrap the can. Now, lets just hope those NOS cans can be reformed.

[Structo]

The old caps are wired in series.

So the total is half the value of one of them but double the voltage rating.

[tribi9]

Thx Tom, another reason I was confused is the extra tab with no markings on my FP cap cans. It's actually another stage at 50 mfd @ 50 V, its written underneath the other values on the side of the can and there is no continuity from that tab to the shell. At first I thought that was the negative. Its all clear now. Thank you all.