Exploding EZ40

[Pete_kaye]

Was working in Pye 178A .When I returned home , this had happened . {see photos}
Obviously , it was off in that time. It uses Rimlock sockets which may explain. Fortunately , I have a spare.

[G6Tanuki]

I've had TV-valve Rimlocks go the same way././././.

[paulsherwin]

I don't think it's down to the socket. The all glass construction of these valves has a weak point where the raised base joins the rest of the envelope. 60 years of thermal cycling causes a catastrophic crack to develop, perhaps aggravated by the valve being disturbed during restoration.

I've not experienced this personally but I've certainly heard about it.

[cmjones01]

It's not just Rimlock valves. I had an ECC83 (I think) do exactly this in the power supply of a Tektronix scope. Switched it on one day and all the power supply voltages were messed up. This one valve had a white getter and when I went to remove it, I found I'd only got hold of the envelope. The electrodes and base were still in the socket!

Replaced it with a modern valve and all was well. The old one was an original Mullard. Yes, even the legends fail sometimes!

Chris

[high_vacuum_house]

I have had the same in an HP UHF signal generator. This was a Mullard ECC81 with a cracked base All other valves were ok.

Christopher Capener

[evingar]

Yep, I had similar with a TV24.

I had got it basically working, switched off and then found it had gone faulty again due to a cracked EF91 gone "to air". That area hadn't be disturbed during my previous activity.

[Geoff 555]

Funny enough earlier today while looking through some valves on the shelf I picked one up that had a white ring round it just at the base, remarks to self 'that looks to have gone to air.'
Just had another look to see what it was for this thread and PROVED what an old idiot I am getting.

The top cap was Missing leaving a nice round hole. Not a lot to be said really except perhaps 'beat that!'.
Cheers.
Geoff.

[Phil G4SPZ]

Some time ago, I restored a Cossor 1071K oscilloscope which had been stored in a damp shed. Three or four of the valves had cracked around the bases and gone down to air. I seem to recall a discussion on here at the time suggesting that damp could cause corrosion that tracked up the pins and cracked the glass base.

[high_vacuum_house]

Could also be caused by thermal shock if the valve was cold and then switched on without allowing it to come to room temperature first.

Christopher Capener

[Refugee]

I once read a restoration story for a big amplifier.
The guy took all the valves out and kept them in a wool lines box while doing the capacitors.
When he came to test the amp one of the larger valves (output/rectifier) had cracked neatly round so that the envelope just lifted off.
I have found valves in equipment that has stood idle for a few years where there is an odd valve gone to air. When changing it the glass just lifts away.

[Tractorfan]

Hi,
In my dim and distant youth, I had a Bush TV43 telly in my bedroom. Occasionally I'd switch it on, only to be met by frame collapse. It was the ECL80 that had cracked across the base. This happened two or three times.
The ECL80 was the only valve in the set that lived in a ceramic valve holder. So, sometimes they can be to blame.
Cheers, Pete.