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A Madcap look at Radio Valves (Thermionic tubes) – part two



While I am on a roll decided to write up part two of this series. Some idiotic things you can get away with when working on valve or tube equipment. (Yes, I forgot to tell you in part one that they are the same thing – American = Tube and Europe, more so the U.K.  = Valve, both thermionic devices). I mentioned the story about the transmitter set incorrectly but how about a disconnected aerial. The ship had a ‘bird-cage’ aerial, see fig one below. These were very popular on merchant ships.

Bird Cage Antenna
Bird Cage Antenna - courtesy RCN

What transpired was that in a serious storm the bird cage uplink had broken free from the antenna through incessant whipping and a crewman wrapped the free lead around the porcelain through-insulator/connector of the emergency antenna meaning to tell me about it during the course of the morning. It’s usual after a storm to check damage but not in this case, either suffering from a barbie or acute laziness I decided to forgo this exercise and proceeded to do a test on the emergency gear – i.e. the emergency transmitter, AKD, auto-alarm etc. There is an antenna switchover unit which allows the operator to select the antenna, main, emergency or dummy. I was the dummy at that stage. Some very strange sounds emanated from the transmitter when trying to test key and much to my disgust the auto-tune circuit failed to tune in. Trying to select another aerial also failed to work so I did the next obvious thing to someone who is oblivious to the hangover lurking and ran up the main transmitter. Now the main transmitter was more than 5 times powerful than the aux. unit on the M.F. band – it still would not tune. Not thinking the obvious, actually the not-so-obvious (who connects the two anennae together) I proceed to test at full power – any erstwhile ‘sparkie’ will tell you that salt is a nuisance and this is what I thought the problem was until the third officer told me that a crewman washing down the ‘monkey island’ (the deck above the bridge) had seen arcing from the insulators leading out of the radio office.  Once this had been sorted out I found the emergency transmitter was faulty – it obviously didn’t like the load but the main transmitter was still 100%. I learnt two things that day – transistors can die silently and if all else fails try the dummy load. I’m actually not trying to belittle myself here – there are numerous reasons why antenna change parameters, salt being one of them – in a storm nobody ventures outside to conduct a running repair. There was insufficient protection to prevent the auxiliary transmitter from going faulty – what would have happened in a real life crises where through lack of power the operator had to use the aux. tx. BTW, the output transistors in the transmitter hadn’t failed, as far as I can recall it had something to do with an automatic shut down of the drive circuit. Marine equipment is mostly very well engineered and I remember this equipment well, made by a very famous Danish company and was notorious for being one of the best makes available at the time.  Modern times have brought out safety features in transistorised equipment which makes them far more reliable than valve equipment from low to high powered use.

But on to more trivial matters, what future is held for tubes in our digital age? Well, it was not that long ago that every TV and monitor that came out used CRTs, magnetrons are still manufactured and used in every microwave shipped unless you are lucky enough to have a Power Klystron which can vary wavelength to cook up anything in your oven 😎 , military spec equipment in some countries are still based on vacuum tube technology which is more robust against an electromagnetic pulse generate by nuclear explosions and finally our audiophiles whom prefer the warmer sound of tubes over solid state technology.

In the late 1990’s many Japanese manufacturers sent their CRT tooling over to China for the manufacture of cheap CRTs and of course thermionic valves – this remains a lucrative industry with China and Russia still manufacturing most of the world’s tube supply. Many audiophiles also complain about the quality of tubes coming from the east but like all things, China only gets better by the day. From my side I haven’t any experience with modern day tubes – I think the costing is crazy but I don’t think a rip-off from a component price point of view, more around what it costs to build an entire audio amplifier. Audio transformers, Chokes and Power supply transformers make projects expensive. Capacitors and resistors – well audiophiles harp on and on about getting the best capacitors but as a rule modern day capacitors are just on overall a way better product than many years ago. Tubes are just not that expensive BUT, and again the big BUT, watt for watt are just no match for semiconductor pricing.

If I had infinite funding I’d stick to semiconductor technology – tubes just don’t match their reliability or efficiency.

End of Part Two.

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