I've been thinking of selling my FET 10/PC phono stage, and given it's almost 40 years old, thought that replacing the electrolytic caps would help the re-sale value. When I started looking closely at it, to get the values, I noticed something extremely odd.... There are two pairs of 220uf caps, which are wired in parallel, but strangely, their polarities are reversed to each other. So the negative terminal of one, is connected to the positive terminal of the other. You can see in this photo, the arrow pointing to the negative terminal on the left cap, the right one has it's arrow on the opposite side. I have no idea why you would do that?
Attachments
It is a bipolar power supply. +, Gnd, -
These are delicate traces. Might be best to sell it as-is, unless it's not functional. If you don't have a really good desoldering tool and/or lots of experience, you could ruin those nice gold traces. I've worked on my FET Ten/PC, FET Ten h/l, and FET Ten/e - all are pretty delicate.
These are delicate traces. Might be best to sell it as-is, unless it's not functional. If you don't have a really good desoldering tool and/or lots of experience, you could ruin those nice gold traces. I've worked on my FET Ten/PC, FET Ten h/l, and FET Ten/e - all are pretty delicate.
But that's the thing, they aren't in series, (+ Gnd - ), that I would understand. They're in parallel. It's the four caps towards the center, not the four in the power supply regulators. In these photo's, I've pulled one of the caps. You can see the traces to the pulled cap and the cap next to it, they're in parallel.
Attachments
Ah, that's an interesting idea... I did put a voltmeter across them, and you're correct, they do only have a couple of mV across them. I haven't tried to sketch out the schematic yet, as I was hoping to find one on-line but no luck yet....
I think I've seen that done to mimic a bipolar cap for coupling. I know I've seen Thorsten do that before.
Pars: Putting to electrolytic's, back to back, in series, will mimic a bipolar, but these are in parallel....
EdGr: I hadn't even thought of intentionally using them to limit DC, as reverse biasing an electrolytic is a sure way to blow them up! But in a feedback network, with limited voltages and currents, I guess they wouldn't be damaged? Interesting....
EdGr: I hadn't even thought of intentionally using them to limit DC, as reverse biasing an electrolytic is a sure way to blow them up! But in a feedback network, with limited voltages and currents, I guess they wouldn't be damaged? Interesting....