# Thermionics in the galley



## Varley (Oct 1, 2006)

My dimming memory suggests that the cathode of a thermionic device should not 'see' the HT until it is at operating temperature (although leaving it for too long without drawing current will 'poison').

My microwave oven goes to cooking mode as soon as it fires up.

Even the magnetron in a Raymarc lasted many times longer than any galley nuke'r I have ever owned. I wonder if this has something to do with it.


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## trotterdotpom (Apr 29, 2005)

Isn't it the anode that gets connected to the HT or am I being picky?

Do they still have magnetrons in radars? I think I saw somewhere that they used something else. 

John T


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## Varley (Oct 1, 2006)

I would say HT requires both plus and minus John T. I was cognizant of which electrode of a valve was connected however circuitously (little sparkie joke there) to which pole hence use of fuzzy 'see',

The wonderful KH's SharpEye was the first commercial marine radar to have a solid state transmitter. S band, the technology then (I don't know now) being too expensive for production (unless for those wanting it to shoot at people with). Japan Radio were testing one similar when I fitted KH's to a Schulte Vessel. I am sure they all must 'do' them now but not sure about X band.

I lobbied for the SharpEye not because of its performance (as type approved it must at least reach par) but without high power electronics (it does not use a conventional Bang/duck finding protocol) it would be more reliable. Unfortunately straddled redundancy and closing of our office but the old man 'phoned me in retirement to let me know how the set was 'doing' (well).

That does not, I think, help with the cooking (not even in precipitation).

(Alright one could have zero and the other but that is being even more pedantic. Oui, vous!).


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## sparks69 (Dec 18, 2005)

"Travelling Wave Tube" comes to mind.
Very expensive I think.

On the reliability of a Microwave oven magnetrons, my parents had an early microwave oven from the time they first came on the UK market. It was an ex demo model from a store in Nottingham and we inherited it when they retired and bought a smaller one and it worked for us until the door hinge broke about ten years ago. The magnet is what I find screws with in the garage when I drop them.


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## Duncan112 (Dec 28, 2006)

I suspect that you are right (although the magnetrons in a radar may well be of better quality than those in the microwave helping the longer life) 

We have got used to instant availability of electronic devices, imagine telling a child of today to wait 5 minutes whilst the TV warms up!! (Or even that TV is only available until 10pm with a break in the afternoon!!)




Varley said:


> My dimming memory suggests that the cathode of a thermionic device should not 'see' the HT until it is at operating tempeature (although leaving it for too long without drawing current will 'poison').
> 
> My microwave oven goes to cooking mode as soon as it fires up.
> 
> Even the magnetron in a Raymarc lasted many times longer than any galley nuke'r I have ever owned. I wonder if this has something to do with it.


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## trotterdotpom (Apr 29, 2005)

Duncan112 said:


> I suspect that you are right (although the magnetrons in a radar may well be of better quality than those in the microwave helping the longer life)
> 
> We have got used to instant availability of electronic devices, imagine telling a child of today to wait 5 minutes whilst the TV warms up!! (Or even that TV is only available until 10pm with a break in the afternoon!!)


Isn't that why everything is on permanent "Standby" mode these days with little red lights wasting electricity?

John T


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## Varley (Oct 1, 2006)

I had always thought that was to enable the target device to be ready to respond to its remote controller and maintain 'volatile' settings data. Not much in the way of valve heaters to 'get ready' and if there were it would be counter productive. As well as ripping the cathode material off when HT applied before it is hot the cathode can become 'poisoned' by being left with a cloud of electrons hanging around like drones (the bee analogy not the small flying saucers) with no current. If you look at the circuit diagram for the MiMCo Lifeguard you should see a resistor across the 'keying' supply to the test oscillator. This is to draw a small current through the valve to avoid the phenomenon as it spends most of its time idle.


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## cajef (Feb 8, 2012)

Comparing the life of a magnetron in a radar with the use in a microwave is not really a good comparison, a radar can be running for many hours continuously quite often days or sometimes on airfield installations weeks whereas a microwave is mainly used for short bursts of just a few minutes.


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## Varley (Oct 1, 2006)

True of course however I think that a period of standby must remain a factor. My last one tripped the supply before the internal fuse cut it although it did still melt. The ceramics around at least one of the 'external' magnetron connections was cracked, looked more thermal than quantum physical. I cannot remember which/both. The makers were proud of its inverter technology (I assume instead of modulating or not modulating it adjusted power with some form of variable pulse length. It screwed up the WIFI/SONOS when cooking so I hate to think what RFI standard it was failing to comply with.


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## J. Davies (Dec 29, 2010)

Mr Varley,

Indeed. Radar magnetrons last longer because their duty cycle is far less than a domestic microwave. Only 1 micro second or so full blast followed by perhaps 1 millisecond rest (a thousand times longer than the on period). Kitchen magnetrons need to blast a KW or so all the time to heat up the food.

Interesting what you were saying about KH Sharpeye. I was service manager for them in Singapore for several years just when Sharpeye came out. There was an internal competition to find a good name for the product. My idea was Pioneer, but they didn't like it. "Kelvin Hughes Pioneer Radar" has a nice ring, but someone in Sales won with Sharpeye.

They did have a patent out on Sharpeye's Doppler process for target detection, but not for the solid state technology, so now every man and his dog are making them, albeit with different detection algorithms. 

X band is still rather expensive because power transistors for 9 GHz are still beyond the civilian market, though of course the military can afford it. S band at 3 GHz is no problem because the transistors are similar to ones found in mobile network repeaters.

By the way, Kelvin Hughes no longer exists as a company. They were bought over by Hensoldt in Germany a few years ago. The KH section specialises more in surveillance and military radar now; the commercial shipping sector is still going but it never really succeeded against Furuno and JRC in terms market share. I think even in the good years, KH was only supplying radar to 12 % of world fleets.

Cheers for now


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## Varley (Oct 1, 2006)

Good morning Mr. Davies,

In Denholm we had quite a bit of KH kit including the 80s NKK Newbuildings for Alcan (the yard would, like us, have preferred to have JRC but even the Japanese will steer away on the basis of contract price and the owners had already paid a penalty for building there rather than Korea without us adding extras that were not high priority). Our perception (a corporate one starting before I reached my desk) was that the kit was good but the support was not. In my day that seemed down to the spares stock being held too centrally. By the time I arrived at Schulte's there was little or no K-H kit in the fleet the Isle of Man operation being wedded to a Liverpool supplier of Furuno's. I have to say that they were afflicted by the same malaise which had become far more difficult to live with. While exemptions by flag and class were still available they now had a higher cost penalty and the charterers and TMSA performance implication militated in the opposite direction. The wedded bliss extended to being forced to apologise to this retailer for my criticism of his principals for their inability to provide spares (their definition of timely in one case being months. He had not changed to the now-time where being without a radar for a month was tenable even to rowboat on the village pond and was also incapable of distinguishing between personal remarks and legitimate complaints).

(That DSM sacked K-H in the supply of accounting and R/Os was down to their opportunist behaviour after CAST went bust. Never again was the boss's demand. Being Ex-Marconi then did have something to do with RTAA being preferentially given to MiMCo and the establishment of a self indemnifying deposit scheme to our mutual protection or should we say assured mutual damage limitation).

Ideally I would have like to see SharpEye S band with Sperry/JRC X band but at the time several industry bodies would have scored us down on that (interswitching is mandated by OCIMF/SIRE which is the sort of thing that happens when you let the operators have a hand in specification. I have never seen any company operational procedure for using a radar interswitched which would seem to be more important when the possibility of a mismatch between the ranges selected on master and slave my be an issue to the observer). Now we are in a realm of sensors and displays being considered as separate entities perhaps that would have been more viable. Interswitching then also tied down the renewal options.

I am sorry to hear the SharpEye did not make inroads into the commercial market. I had great hope for it and its 'home grown industryness'. I follow Barry Jones on Linked-in.

(Did you come across Denholm Agency's delightful and ever helpful Elsie Koh)?

David V


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## J. Davies (Dec 29, 2010)

KH are doing well under the new umbrella. They are definitely leaders in surveillance and military radar, using Sharpeye technology.

I did not meet the lady you mention, unfortunately. That reminds me of a 7-month stint I did on a VLCC back in the '80s, trading Gulf to Japan and back, _ad nauseum._ We slow-steamed off port limits Singapore for bunkers and supplies, and once an intrepid lady representative from the chandler came on board for an afternoon by offshore launch. Hardly seeing women at all for months we were transfixed and plied her with drinks in the bar. After she departed in the evening, before we were away on passage, the 3rd engineer was caught sniffing her bar stool. Disgraceful.


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## trotterdotpom (Apr 29, 2005)

I received a telegram from KH querying some spare part that had been ordered. It was signed G. *** (Miss). I replied to the message and added "What does the "G" stand for. In no time at all, back came "The G is for Geraldine". A couple of post cards and letters followed and before long Geraldine had moved back home to Dublin. I found myself at Riversdale doing a course and was eagerly planning a trip westward into the sunset. I now live in Ireland and have 19 children ... just kidding, I met another one and never bothered going, sometimes wish I had though.

John T


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## Varley (Oct 1, 2006)

You Devil, John T.


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## sparks69 (Dec 18, 2005)

My experience with Magnetrons in Decca Radars was that you received a new Mag in the PG, fitted it as you left the Gulf heading for LEFO on one boiler i.e. about 12 knots. Checked it for range in the Mozzy Channel - OK. By the time you got to the Canaries you could see the mountain before the radar picked it up at about 15 miles. The radar had been running continuously since leaving the PG (as recommended by some judge in an enquiry). That was about 1000 hours !
Did these trips for a number of years and many times I requested a regular supply of replacement Mags but was always met with "Decca says they last x number of hours so there must be something wrong with the radar"
I believe one VLCC diverted to Gib to pick up a Mag as "you had to have a working Radar going through the Straits of Dover" Company was not amused !
Mags were 3cm EE M515 made in Lincoln.


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## Varley (Oct 1, 2006)

I had a figure of 3000 hours in mind (and found a reference that agreed just now). I also have a memory of 'third generation' magnetrons from EE with 5 k (?) 'lifetimes' and with a guarantee.


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## trotterdotpom (Apr 29, 2005)

sparks69 said:


> My experience with Magnetrons in Decca Radars was that you received a new Mag in the PG, fitted it as you left the Gulf heading for LEFO on one boiler i.e. about 12 knots. Checked it for range in the Mozzy Channel - OK. By the time you got to the Canaries you could see the mountain before the radar picked it up at about 15 miles. The radar had been running continuously since leaving the PG (as recommended by some judge in an enquiry). That was about 1000 hours !.....Mags were 3cm EE M515 made in Lincoln.


Sounds like those old time captains were right with their "It won't work when we get to the fog" mantra.

Haw haw. Don't tell me Rustons made magnetrons!

John T


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## sparks69 (Dec 18, 2005)

Varley said:


> I had a figure of 3000 hours in mind (and found a reference that agreed just now). I also have a memory of 'third generation' magnetrons from EE with 5 k (?) 'lifetimes' and with a guarantee.


Yes in the mid 80's they were saying 3000 hours but I never actually found that this was true. The problem was that you couldn't send duff Mags back to UK due to airline restrictions on magnetic materials at the time.
No doubt they made them better after I packed the sea in.
Must ask one of our walking group who worked for EE in Lincoln making the Mags.

JT - Rustons didn't make Mags, EE did !!


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## Varley (Oct 1, 2006)

I think a Ruston's PRF would require a very very slow rotation. Would it transmit on suck, squeeze, bang or blow?


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## trotterdotpom (Apr 29, 2005)

sparks69 said:


> JT - Rustons didn't make Mags, EE did !!


I was just kidding - referring to the disastrous Ruston AO main engines. I learned how to live without a flushing toilet because of them. Didn't realise that Magnetrons came from Lincs too.

John T


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