Pilot_DAR wrote:
I don’t think that civil users would accept it, once they had had a taste for the precision of GPS.
eLoran is supposed to have a precision of ±8 metres which is good enough for LNAV/VNAV.
I’m surprised that there are quite a few LORAN stations in Middle East an Asia (Saudi Arabia, China, India, South Korea)
I am sure Loran will remain totally unused all the time GPS is working, which it is some 99.99xxxx% of the time.
Even in the early days of GPS, when some US avionics firm did a box which did “RNAV” using composite sources, nobody bought it. And if you look at the cash cows which GPS boxes are (a GTN, parts cost say $300, selling end user for say $15k) any Loran box would not cost less. I am sure nobody would bother to make an aviation product.
You are more likely to get a triple-FOG box which emulates a GPS antenna (actually an NMEA stream) for loss of GPS situations. These have been around for years; cost 4-5 figures. Some previous threads.
Peter wrote:
You are more likely to get a triple-FOG box which emulates a GPS antenna (actually an NMEA stream) for loss of GPS situations. These have been around for years; cost 4-5 figures. Some previous threads.
Do you mean INS? I’m surprised that those are not made mandatory for all IFR flying. If they were, the cost would really go down! :)
Yes. But they will never be cheap. The cheapest civilian (uncertified) box is probably around 5k now (not checked for years).
Just organising all my books after the move, I found a textbook on avionics – heaven knows where I got it. DOn’t have the details as I’m away from home again for a while. It was published in 1986 but that must have been a reprint or a very minor revision, because all of the circuit examples use valves (vacuum tubes). It must originally be from around the early 60s I would guess.
I’ll post more and some pics of the circuits when I’m reunited with my books.
This is currently installed in a Socata TB10, S/N 168, based in Germany, now sold to Russia.
fwiw I found the book again. It’s called Aviation Electronics, by Keith W Bose, published by Jeppesen in 1983. It’s the third edition, don’t know the original publication date but it must be pretty old. As I said nearly all the example circuits use valves/vacuum tubes.
I think valves (vacuum tubes) were last used in avionics in the 1960s. My guess is that the last refuge of valves might have been in the output stage – the RF output of say a transponder – before RF MOSFETs arrived.
I used to design with valves back in Czechoslovakia when I was a kid, 1960s, EF80, ECC83, EL84. High voltages everywhere and I got countless shocks. Here in the UK, used to build pirate radio transmitters using transistors but with 807 valve output stage for a few hundred watts of RF power – with enough harmonics to cover the whole MW band without anyone having to tune their radio 
Really lethal, with a 700V DC supply. Valves are great, and can be made rugged enough (although the rugged ones, metal cans, were milspec and hard to find). Valves have a very similar behaviour to JFETs, with the inconvenience of needing a heater supply.
Funnily enough the KLN90B uses a CRT (a valve!) for the display. I have the MM for it, and it is a tour de force of circuit design and documentation. I think King contracted it out since it surpasses even their high standards of that era. The great advantage of a CRT, over an LCD, is that it works at any temperature. I think that issue must have been largely solved with modern avionics, and hopefully not just by heating the LCD…
The Russians carried on using valves in avionics for longer. Opinions differ as to whether it was because of their superior EMP resistance, or because they just didn’t have good enough transistors. The MIG25 used an extraordinary valve, the 6C33C-B, as a voltage stabiliser. It will happily pass 0.5A at 120V. They have been used more recently for output transformerless (OTL) audio amplifiers. Back in the 90s I built several valve amplifiers, and my daily listening is still a pair of OTLs but using 6AS7Gs (lots of) for the output stage.
