Replacing selenium rectifiers

[Michael Maurice]

When repairing the Pye Black Box featured in this thread it became obvious that the selenium rectifier had to be replaced. Giving around 50V HT it simply wasn't doing its job.

The rectifier was housed in a small metal can which was bolted to the chassis.

So I removed it and by opening up the tabs, I could remove the encapsulated rectifier.



I obtained a suitable rectifier from Cricklewood Electronics a 610.

This would comfortably fit in the metal can but with too much room.

I found some epoxy that you could mix up which would act as a filler.



I aligned the positive of the bridge rectifier with the + printed on the metal of the corner and fitted it and the epoxy into the can.

This is the result:



And here it is fitted onto the chassis. Note the tag strip to the right to which the limiting resistor is mounted. If a half wave rectifier is fitted, then cut off the - tag and one of the ~ tags.

Job done and with pictures, very handy.

[paulsherwin]

You could also fill the gaps with hot melt glue, or even cheap epoxy glue from Poundland.

[threeseven]

Neat job, well done.
Another alternative mounting material is black automotive silicone RTV. I use that for many electronic tasks, like mounting Avo glass, dial glass, panel meter glass, holding components etc.
Just mentioned as another option that may be appropriate.

[Radio Wrangler]

I can't think of where, but I seem to remember reading warnings about handling overheated selenium rectifiers. It could be a corrupted memory, but perhaps worth checking.

David

[Silicon]

Please note that that some of those epoxy putties claim to contain metal and therefore are not insulators.
They might be good for thermal conduction of heat from an insulated device like a bridge rectifier.

[threeseven]

Yes, that would apply to the plastic metal type products which I've used to repair castings on motorcycles. It never occurred to me to test it for continuity, I will try the next time I use it !

[McMurdo]

Plastic padding chemical metal has a resistance of 10 to the power 14 ohms per centimetre...like most fillers, it's polyester based.

[Herald1360]

Shouldn't that be a resistivity of 10^14 ohm.centimetre?

[John Caswell]

Hi all,
Yes as RadioWrangler (David) says handle damaged selenium rectifiers with care it is a nasty element.
In my servicing days (long gone) we always handled damaged ones with gloves, and I remember the council ripping a pre-fab apart to try to find the smell from one that had failed in a TV!

John

To quote some pop band 'Oh Oh that smell', they say you never forget the smell of death, luckily I have only smelt (?) selenium rectifiers failing (well one, that was enough!).