Hi,

I have a what I hope is simple question.

I'm replacing caps, and there's 3 single section Ducon can electrolytics (3 pins but 2 soldered to chassis) but the schematic doesn't seem to indicate polarity.

How can I identify polarity so I can correctly replace them? I've noticed that there's a rivet on the can... is that an indicator? If so, is it + or - ?

The pins that are soldered to the chassis will in this case be (-)

In some cases, such as where back bias is used, the (-) doesn't go to the chassis but to the HT CT of the transformer. Where this is done with a can, the can itself is insulated from the chassis.

Thanks Ian,

Much appreciated.

In retrospect, I suppose it makes sense that the negative is the chassis...

Skeptical: Would be nice to see the circuit. A back bias resistor/s would see a cap of around 40v 25μF positive to chassis neg to CT. CT is the most negative & the chassis positive relative to it, in this case.

Depending on the manufacturer it would then be plausible that the can is floating with both HV filter negatives on the CT and the positives either side of the choke / resistor if in B+.

Sometimes in those cans the low voltage cap was the the OP valves cathode bypass if it is self biased (cathode resistor fitted). In that case the cathode is positive & the chassis neg.

Hi Marcc,

Schematic can be seen here: https://ibb.co/TRtz22n

That is unusual for Astor. Its not back biased & is conventional Two filter caps negative to chassis & the other as I expected the cathode bypass for 6V6. I would tend to use 600V types on the "B".

Test point is for an AC voltmeter with 0.1mfd series cap. Some meters had that cap & the terminal was marked Output ( E.g) Peak 200H with new cap fitted inside it).

Hi Marcc,

I got the caps from justradios.com. The 16μF caps I purchased are 600V. The other Can (#22 in the schematic) is a 25μF 40v which I'm replacing with 25μF 50v which connects to the 6v6.

From the sample schematics for 5 valve radios I've seen online, Astor seem to have taken a fairly textbook approach to this one, which from your comment isn't typical for Astor? - I probably should be thankful to them as this IS my first rodeo, haha..

I have another page which shows the conditions of test and the voltages I should be seeing on the valve pins. That'll be a big help with troubleshooting, but last time I powered this thing on, it worked, albeit with a very loud hum that almost drowned out the radio - which is why I'm replacing all the electrolytic and paper caps. (hopefully the tubes are all ok)

I've always found justradios to be excellent
One day I was fixing my Kriesler chassis and the new parts came from justradios .but there was a boo boo in the order of one cap which is a bit hard to get here, it was a poly for the sound ,anyway he sent me a pack to make up for the boo boo.
I'm no guru with electronics,but all the caps and resistors Ive bought from him have been fine, pete