Old electrolytic capacitors

They leak more, so removal is generally a good idea.

Ta mate.

I'll leave it in, for appearance, but disconnect it.

Replace ALL the capacitors, whether faulty or not, ie remove them completely and fit new ones.

They dry out over a period of time and have a tendancy to explode!

sponix

That should work fine - once disconnected, they should happily sit there for many years.

I've done a few of these in the past. Usually the hum can be cured by addressing one, possibly two capacitors depending on the design. Some had two capacitors in one can.

Often I was able to obtain a new C which would fit the old space, possibly with adding a clip to hold the new one.

Otherwise, the alternative is to fit the new one under the chassis, if there's room and a small enough component can be found. I clipped the leads off of the old one.

Another phenomenon I've seen is that the disk where the terminals are had split and the contents had started to come through. Unfortunately, that radio had a glass front panel and the works inside could be seen. This was long before valve hifi amps which had this. In that case, I did a kind of electronic root canal job and removed the C, dug out the contents and returned it empty into the chassis. A new, smaller capacitor was araldited inside the case of the old one. Cosmetics maintained.

It's also worth looking out to see if there is a selenium rectifier. These are prone to fail as well, typically if there has been some kind of other component failure resulting in overload. When they do, the smell is indescribable. Escaping throwing up is pretty difficult. Again one can disconnect and replace with some suitable silicon diodes.

Try rec.antiques.radio+phono and search for 'recapping'

It has worked.

Very well indeed.

Actually it don't look like they were leaking that much, but the new capacitors showed a huge amount more capacitance (with an ohmmeter)than the old ones did.

So it wasn' a MISTAKE to disconnect the old..and it made tie-wrapping the new ones in place a lot easier :-)

Arrggh. All these AC/DC sets with directly heated heaters and little UL this that and the other glowing in the dark...

Brings a tear to the eye it does.

If anyone wants spare valves I bought a whole bunch off E-bay - UL/UY/UCC/UFB etc.etc.Got some PF valves as well - those are ex TV I think :-)

Slightly off the original topic but I have the same problem with a new-ish CD clock radio that I now use in the garage for time and music. It has a mains hum (heard throught the speakers so must be getting into the amp stage), this happens even if the CD or radio is switched off. I have thought about tracking down the hum and trying to fix, could it be some faulty caps?

Paul

Yup. Thats the bunny - 50uF +100uF 275V DC crimped into the chassis

Tried, but it was costly and nothing really fitted...

Well I unsoldered the two tags, bent em flat, and tie wrapped three 47uF

I nearly did that..but it was too much like hard work and they didn';t QUITE fit :-)

Nope. UY85 IIRC. Nasty half wave jobby. Ive replaced nearly all the valves - got a job lot for 20 quid - but really the only faults were those capacitors and corrosion on the switches and valve pins. Contact cleaner sorted that.

This is not a classic set..its just an old AC/DC set from the 50's..a favour for an old widower who used to like to listen to it.

Nah. The rest are fine.

There aren't any more electroltyics anyway as far as I can see.

Sounds like you might enjoy a site put together by an acquaintance of mine - usual disclaimers:-

I think the archers finished in the 60's? ;-)

-- Sir Benjamin Middlethwaite

It's actually amazing how good the build quality was. I've often found the most troublesome component to be the variable capacitor in the tuning. Typical problem is that the set has been left tuned to one station for years and the contacts have corroded. Then there's crackling. I disassembled one once to be able to get to the contacts. Never again. It was a bastard to get back together without bending the vanes.

These sets often have great sentimental value and memories and sound of a bygone era - e.g. listening to the Archers or World at One etc.

I see you're not that old..."Tuning capacitor" was the term, way back then. :-)

-- Sir Benjamin Middlethwaite

|I am busy refurbing an old valve radio for a mates dad. | |It works OK, but hums a bit.(the radio, not his dad) | |I have some new electrolytics for the power supply, and am wondering |whether to remove the old mans capacitors and put in new ones, or simply |wire the modern replacements across the old one. | |In short, so old electrolytics simply lose capacitance, in which case |adding some more can only be good, or do they also develop extra |leakage, in which case removing the old (electrically) is to be preferred?

On *very* rare occasions old electrolytics explode. Best replace them.

What I mean is I'd remove them all from the circuit..you can leave them physically there to maintain the look of the set.

You can still buy the old style variable capacitors:

Don't leave the old ones in circuit. Leaky bypass ones can cause nasty noises and faulty ones across the HT can explode.

Of course, if you had an ESR meter, you'd know which ones need replacing...

Depending on the individual components you may be able to dismantle the old capacitor and remove its gubbins, leaving enough space to fit the replacement component inside the case of the old.

Owain