When capacitors go bad.

[G6Tanuki]

My new "dabble when I'm not busy" toy is a 1950s marine radio [RX has 12-volt-HT valves and a big single-ended class-A transistor for audio output, EF89/6L6/6L6 on the RF side, vibrator and two EZ81s for the HT].

So far I've got the RX to make noises - though both the aerial-coupling windings on the front-end have clearly been used to pass some significant current and are now open-circuit hence the poor thing is as deaf as a deaf thing. Experimental rewinding is clearly needed.

The transmitter - well, I've spotted a major "ooh nasty" - here's the pair of capacitors used to resonate the secondary of the vibrator-transformer: one capacitor has entirely shed its outer casing, the other is split and there's molten wax all over it.

[mark pirate]

one capacitor has entirely shed its outer casing, the other is split and there's molten wax all over it.

To say I have seen worse is a bit of an understatement, check out the photos of this ex Dubilier cap, this went off with such a mighty bang, that a replacement pair of underpants were required

Mark

[G6Tanuki]

Ah, that looks to be a lovely example of the genre "Noise-Emitting Capacitor".

[Not to be confused with that other device - rather rarely encountered today - the Smell-Emitting Diode].

[Lucien Nunes]

Your capacitor shed its encapsulation but the wound element stayed in place. This one in an Abbey tape deck did the opposite - the cardboard tube remained attached to the leadout but the capacitor itself shot out of the end. A capacitor-emitting capacitor.

Lucien

[HamishBoxer]

Try a main smoothing cap (bomb) going off in a new Thorn 950 series TV back in the seventies in the DER showroom, Silver Street, Doncaster where I worked. That's a real bang.

PS. It spilt the wooden cabinet.

[Radio Wrangler]

I think it's something they do to distribute seeds and reproduce.

David

[G6Tanuki]

Originally Posted by Lucien Nunes

Your capacitor shed its encapsulation but the wound element stayed in place. This one in an Abbey tape deck did the opposite - the cardboard tube remained attached to the leadout but the capacitor itself shot out of the end. A capacitor-emitting capacitor. Lucien

*grin* I've had a few spit out their insides: the TCC "Metalmite" ones with the aluminium case crimped to the rubber bungs in the ends go off with quite a bang.

I just did a test of the 'exposed' capacitor shown in my first posting: hooked it across a 450VDC supply and it passed around 35mA - enough for it to get painfully hot after ten seconds!

[HamishBoxer]

The wax French are the best as when they overheat through leakage, it's very easy to pull out the guts and restuff.

[G6Tanuki]

Originally Posted by HamishBoxer

The wax French are the best as when they overheat through leakage, it's very easy to pull out the guts and restuff.

Must admit, I've never bothered with restuffing: I prefer functionality over appearance.

A friend some time back was rebuilding an old radio and automatically went through it replacing all the apparently-old-and-suspect capacitors with modern Polyester beasties. Some weeks later he met the radio's previous-owner-but-one who told him "I patiently restuffed all those!".

The radio in question continues to work. There's a "Zen" metaphor in there somewhere I'm sure.

[Station X]

I do restuffing on some sets. I leave a note inside the set to say what's been done.

[HamishBoxer]

Don't do much restuffing on sets through the workshop but there again do not get many French ones'.So in the main G6T you are correct.

Though Graham is also right to leave a note inside.

[TrevG3OAD]

I've had endless fun replacing all the small tantalum caps in some 1980's test-gear which worked fine until put into unheated storage over a very cold winter. A touch of frost did them a power of no good.
Trev

[camtechman]

Originally Posted by HamishBoxer

Try a main smoothing cap (bomb) going off in a new Thorn 950 series TV back in the seventies in the DER showroom, Silver Street, Doncaster where I worked. That's a real bang.

PS. It spilt the wooden cabinet.

I used to work in the Quality Assurance & Accelerated Soak Test Department at Thorn's main centre in Enfield, Middlesex (known by the locals as "Fergusons") in the late 60's to early 70's.

We had many different variants of early colour TV's on long term & accelerated soak testing all on a 24 hour non stop cycle.

Eventually we became imune to jumping out of our skins when caps used to explode, sometimes several sets in short rotation. Then, as a junior, my job was to remove the offending cap/s & debri, fill out a technical sheet to record various data about the item/s and pass it on to the Technical Evaluation department.

Working in there was a nightmare, not because of exploding caps but also the high temperature of the unit & more so because of the static build up.

Once we were given a "VSP" (Very Special Person) set to give a thorough soak test to and after replacing a few faulty parts during it's soak test period, the set was passed to the cabinet fitting section. A hand made, solid teak cabinet was fitted & Sir Jules personally delivered it to 'Buck House'.

Six weeks later a very burned & smoke blackened set was returned back ! Whoops!