Hi All,
A quick question about what to do with the negative pole of an electrolytic capacitor in the case of a 'floating ground' (if I'm expressing that correctly). The majority of the time, I connect replacement electrolytic capacitors to chassis ground; I often use the retaining tags for the 'can capacitor' which one finds under the chassis.

I now have a nice little Sparton 6A-66, which apparently has a 'floating ground', where the chassis itself is not the ground.

The question: Where would I attach the negative end of the electrolytic?

Don’t ever assume the chassis is the B- ground. A lot of radios do have a B- buss line that is not connected to the chassis. If this radio has a can type filter capacitor, there is probably an insulator between the chassis and the negative can. You can use the negative lugs on the old filter can to tie the new capacitors negative leads to. This would be the B- line that is a common tie point.

:Don’t ever assume the chassis is the B- ground. A lot of radios do have a B- buss line that is not connected to the chassis. If this radio has a can type filter capacitor, there is probably an insulator between the chassis and the negative can. You can use the negative lugs on the old filter can to tie the new capacitors negative leads to. This would be the B- line that is a common tie point.

Hi Warren,
Sorry for being naive, but how would I identify the B- bus line by looking at the can capacitor from below. I could attach a picture of the capacitor if that would make things clearer, but what I seem to have are two B+ tabs coming out of the bottom of the can (one is 20uf, 160V, the other 40uf, 160V according to the schematic and the markings on the side of the can), with wiring to various parts of the general radio circuit.

There is a third tab, also with wires. I just want to make sure this is the B- point before I start attaching replacement electrolytics to it. This third tab has no direct connection with the chassis itself, I think.

I don't think I've encountered a floating ground radio before.

Cheers,

The marking on the can itself would indicate the terminals of the capacitor. The 20 MFD and 40 MFD should be clearly marked. The 3rd lug would have to be the negative that is common to both capacitors. You would disconnect the wires from the positive terminals of the old capacitor. Connect the new capacitors positive ends to the wires. Leave the wires connected to the old capacitors negative can, connect both new capacitors negative leads there. ( Note ) with an ohm meter connected to the negative leads on the can, you can prove this is the B- by the schematic.