Very rare pictures. Can you identify?

[Heatercathodeshort]

This evening during preliminary work on a future project I observed this very rare phenomenon and was lucky enough to catch it on camera. I have been working with television servicing since 1960 and have seen similar but never anything quite so defined as this. Can you identify what you are actually seeing in these two shots?
I will post the preliminary details of the start of the project and hope to finish it in the autumn with full postings. Regards, John.

[Nicklyons2]

Last time I saw something which looked like that it was using a 'fine beam tube' at college.

I suppose I'll look a 'berk' here by being miles out but I'll have a stab - if that is a glowing cathode on the right; is the purple glow focused & unfocused electron beams in a gassy tube? or the beam hitting imperfections in the glass?

[Studio263]

Gassy old tube? Go on, give it a bop!

Even though this is on a much smaller scale (just in front of the cathode?) it reminds me of when I first had a 17" Philips 320 working, there was a similar cone of blue visible behind the scan coils. Of course this is just the screen illumination visible through the glass where the internal coating is a bit thin, but as a beginner I of course thought that the tube had air in it, odd because the picture was really good (as they always are).

Looking at the picture again it is odd that you can see so much of the internal structure from that angle, is it an electrostatic tube perhaps?

[Heatercathodeshort]

Hello Nick,
You are absolutely spot on! A few weeks ago a receiver I have been looking for since the early 60's turned up. Sadly the tube was faulty and I guess this rare little receiver had been written off around 50 years ago. The tube is a very unusual Brimar [Cintel] C12B but a request on the Forum produced a superb example from Trevor. [TNC] This story is for another thread and will be completed when time permits.
Back around 1960 to prove the original tube was faulty, I guess a service engineer had removed the Bakelite base to check the wire tails were making good contact with the base pins. The vacuum and the heater assembly appeared intact so I connected my tube tester/reactivator. [Bertha] It showed zero emission and nothing would stimulate a microamp of life.
Last night in an attempt to access the very clean chassis I decided to wake the line output stage from it's slumbers. My successful attempt resulted in the correct figure of 10kv appearing at the EHT rectifier.
Curiosity killed the cat they say so I decided to connect the baseless triode crt into circuit using crocodile clips.
When the EHT built up and just for a very few seconds, a strange defocused 'blob' appeared on the screen. It really was quite spooky! Examination of the gun assembly in the incredibly long neck, revealed the display in the pictures. Ionization caused by a few molecules of air in the faulty tube had made visible the actual electron beam that can be seen streaming from the tiny hole in the grid assembly. The pictures show the fan shaped 'spray' and the focused beam obtained by adjustment of the electromagnetic focus control.
The EHT current was of course very heavy under these conditions causing strain within the EHT rectifier 'bell'.
The display was quite unlike the usual Argon coloured discharge obtained when the gas level is somewhat higher. [Probably similar to your's Mark]Complete lack of a vacuum will produce the classic EHT arcing within the electrode assembly, note arcing, not a glow. Thanks to Trevor I have a good C12B [picture] to complete the restoration. A new thread will be started in due course. Regards, John.

[Heatercathodeshort]

Tim also had the answer and posted while I was writing the explanation. J.
PS The tube is so long I have posted the picture lengthwise. The photo programme squashes the height if I turn it vertically!

[jjl]

John

Some years ago I worked at an establishment just down the road from you where ion implant machines were made.
Some of these machines had inspection windows part way along the beamline through which the ion beam could often be seen. Running an argon test beam showed a very similar blue line to that in your photos.

John

[Heatercathodeshort]

Thermionic emission. A miracle. John.

[line sync]

A nice looking c.r.t , shame its no good.
I thought the blue glow was inside a c.r.t but had no explanation for it.
I look forward to the new thread john as always.

Robin

[Refugee]

I have seen the same blue glow in an output pentode. It went to air some time later and it was an expensive one to replace too.

[Philips210]

Hi

I remember back in the 1980's a Thorn 3500 produced a very dim raster and had an odd blue glow in the neck of the tube but I never found out for sure what the problem was as the set wasn't repaired. I think I condemned the tube for this fault, it was low emission anyway, but I had my doubts.

I think there was some mention about the tripler causing an odd effect like this but didn't understand the fault mechanism. What could cause this other than the tube itself?

Regards
Symon.

[Heatercathodeshort]

Originally Posted by Refugee

I have seen the same blue glow in an output pentode. It went to air some time later and it was an expensive one to replace too.

Just a thought to prevent guys scrapping particular output pentodes that have a blue glow. Certain types, particularly line output valves often show a well defined [focused]faint blue glow within the electrode structure. This is quite normal and can be ignored. The E/PL38 comes to mind and a similar glow is often seen within the Mazda range of line output valves. In the audio field the EL84 often has a blue 'garden gate' pattern visible through the anode apertures, again quite normal. I just hope I have not started another craze with the audio brigade requesting 'garden gate' EL84's...
Almost all the remaining valves should not show a glow of course. I had an AC/PEN recently that really should have been given pride of place on top of the Christmas tree and an EL33 likewise, both useless.
If anyone is kept awake worrying about loss of vacuum in his output valves, please send them to me for burial in a quiet spot here in West Sussex. Regards, John.

[Nickthedentist]

There's a nice video about online of a Philips very high-power PA amp playing some organ music, accompanied by a lovely blue dancing glow from the valves.

Nick

[cmjones01]

I think they're mercury vapour rectifiers, which would explain the dancing glow, but I could have mis-remembered.

Chris

[ScopeMonkey]

I think Nick's talking about this video, but it seems there are quite a few on YouTube of this model of amplifier. Seems like the blue glow is indeed from the rectifiers.

Ed.

[Nickthedentist]

Sorry for being thick :-(

[PJL]

The tube has managed to hold on to most of its vacuum for all those years...I wonder if there is any chance it might recover if powered up for a while? Maybe the emissions would just die away as the cathode gets polluted or with EHT the phosphor might be annihilated by the ions?

[Hybrid tellies]

I have seen this effect on the Pye 691-697 chassis when a crack on the CDA board removes the HT supply to the PL802 Luminance output stage causing the CRT to conduct heavily through all three cathodes. Quite spectacular and accompanied by a loud howl of protest from the line output stage.
More recently in my Decca Bradford the PL509 had this glowing cloud of blue haze inside the glass envelope. It would continually vary in size and shape as the valve warmed up and with load. It was like this for years before it started to give any noticeable effects.