July 14, 2016 at 12:03 pm #1560
After four decades of ‘riding the rocket’ in the electronic industry, I had kind of resigned myself to the idea that I’d never be able to keep across all the new technologies popping into being.
But I guess I never imagined that I should also resign myself to not being competent in all the older electronic technologies either…
Then the lady at the local café gave me a 1950’s-era valve radio to sort out for her old-timey shop, and so began a whole new branch of humiliation in the study of the things I don’t know.
This ‘made-in-Australia’ radio bears out the old adage that ‘beauty may be only skin deep, but ugly goes to the bone’. Ugliness lives under that chassis!
After doing all the obvious things like changing out leaky paper and wax capacitors, installing an aerial, fixing the tuning pulley and such-like trivial stuff, still no reception. There are only five valves, ferChrissakes!
What I lack in valve-era technological know-how, I make up for in friendships with older engineers from that era. So I found me one of them.
It’s taken seven months, an introduction to valve-testers and heptode superheterodyne mixing, green spot disease in old enamelled coils, the impact of screen grid resistor failures, arcane test procedures and a growing wonder at just how clever these old bits of kit are at plucking a signal out of the ether.
I won’t be attempting any more such fixes; 250V DC is just too scary. I’ll stick to repairing my collection of old Tektronix oscilloscopes…
But if you ask me about my expertise in electronics, I’ll tell you that I love it all, but only understand a tiny fraction.
July 14, 2016 at 12:51 pm #1561
You are driving me to distraction. I recall playing with valve radios as a kid. They were retro technology then. I wanted to show off with my esoteric knowledge of the ‘eniode’ with its nine electrodes (7 grids) but just couldn’t find it in google. I was sure I was not dreaming. I’d long since thrown the data books away but I found a book online and it was there. I had the spelling wrong which would come as no surprise to any of my teachers over the years. It is an enneode or nonode.
It produces an output proportional to the phase difference between two of the grids and as such was used for FM radio detection.
I never had one as a kid – but I wanted one. Now I can buy one on Ebay for eight euro’s but I don’t want one. It’s marked new – if a part that was made in the 1960 can be called new.
Take care with those tektronix CRO’s though – they’d have anode voltages of some thousands of volts and my one an only substantial experiment which involved using my body as an electrical conductor was picking up a CRO display tube by the socket while the system was still powered up.
July 15, 2016 at 1:01 pm #1564
“Driving you to distraction” doesn’t sound good…
Is it all those suppressed memories of bygone days?
So I also did my homework, and the valve in question is an EK32 ‘octode’, rather then the ‘heptode’ I’d thought it was.
This has six grids in three columns, and some of those are used as plates (I’m told).
This valve was used in the rf front-end of the radio, acting as both an amplifier, a the local oscillator and the down-mixer for the following if stage.
So the lesson here is that the quality of thinking and the novel ideas of good engineering don’t change with time; just the technology that we have to work with is different.
Interestingly, vacuum tube technology lives on in the travelling-wave guides used in satellites and in the development of vacuum channel transistors for use in terahertz equipment for directional high-speed communications and hazardous-materials sensing.
Finally, you’re right about the high operating voltages inside the old Tektronix valve scopes, but those are beautifully-crafted pieces of engineering, well-documented and easy to move around in safely. And even back then – in the 1960’s – they understood that the electron beam in a vacuum had a finite speed, and so developed distributed electrode methods for high-speed analogue CRTs (cathode ray tubes).
Knowing your electronics history can help with modern design work.
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