Hi peoples,
My name is Ryan, I have been collecting old radios for several years now, mainly because I like preserving objects from the past, and of course the fact that they look nice on the shelf doesn't hurt..
Anyway, I have about 40 or so of them and two old valve TVs.. But I know very little about the valves themselves.
So I am trying to fix the old (1957?) Pye Technico TV that I rescued from the op-shop and I think the IS2 valve is shot. There is a blue glow inside it that appears when the set has warmed up. I have a brand new IS2A valve, but don't know if it is compatible. Can I swap it over, or will this cause the blue smoke to escape?

Thanks for your help,
Ryan

G'day Ryan,

A valve with a blue glow is referred to as being 'gassy' but this doesn't mean that the valve requires replacement. The glow is caused by electrons in the valve hitting the glass envelope in a similar way to how those 1980's plasma lamps work (the glass balls with the lightning in them).

It is sometimes said that the blue glow is just a visual confirmation that the valve is working. I must admit that the first time I saw this phenomenon some years ago that I was a bit apprehensive and thought the valve was going to blow up in my face. There's nothing to worry about though.

My 'good book' (Philips valve data) does not describe the 1S2 as it was printed before television took off in Australia, though according to the link below it is an Extra High Tension (EHT) rectifier valve.

http://www.radiomuseum.org/tubes/tube_1s2.html

Unfortunately I cannot confirm whether or not the 1S2A is a suitable substitute, however there are a number of 1S2's available on Ebay if you need one.

Hello Ryan. A gassy valve will have a blue glow inside the electrodes and needs replacing. Some types will produce a glow on the glass by stray electrons hitting it and causing it to fluoresce, similar to a cathode ray tube. It's often a blue green colur and the 6BQ5/EL84 is a type prone to showing it. This is an indication of a tube with a very high vacuum and nothing to worry about. You can use the 1S2A, the sufix usually indicates an updated, improved design.
Don Black.

I have an old Williamson amplifrier that uses a pair of 2A3's in class B. These valves have a real 'hard' vacuum and produce a dazzling modulated purple light show around the glass envelopes when pushed hard. Initially I thought these triodes were 'sick'. Bought a pair of new ones (NOS) with the same result. Don is right and the 2A3 is a good example of the effect.

The 1S2 and 1S2-A are technically identical. The 1S2-A is a variant, having a chemically treated envelope for use under humid conditions. So it is a direct replacement.