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Discussion Starter · #21 ·
Progress on Kelvin Hughes - at last!

It’s been all go at the Museum since we closed last October. A lot of progress has been made on the Kelvin Hughes, but there are still a few issues to resolve before it can be turned on. On-Site work at the Museum has stopped as it is now in lockdown owing to the Coronavirus. My wife and I are keeping ourselves as isolated as possible, but making sure we get a few hours outdoors exercise each day. On the last day that I was able to go to the Museum I brought various bits and pieces home for repair or modification: The Challenger synthesizer to be modified for Amateur bands; Kelvin Hughes HF antenna Tuner, Screen voltage supply and HT timer; faulty spare Marconi Oceanic receiver to test some PSU mods before installing the mods on the good working one; tons of do***entation and interpretations to update. Not to mention my own projects - so I won’t be bored!
Now focus! Kelvin Hughes! Back in 2016, when the equipment arrived at the Museum we soon had the Receive side: Main Receiver, Reserve Receiver and AutoAlarm working. Had to “borrow” the Synthesizer power supply from the Transmitter to get the Main receiver synthesizer working. An initial inspection of the Transmitter showed that some parts had been robbed from the IF/HF antenna tuner: some high voltage capacitors, the antenna loading coil, and antenna coupling capacitor. (see pictures). Over the last three years I’ve collected together suitable replacements as and when I’ve stumbled across them at rallies etc. The pictures show where the missing parts go, and the replacements fitted.
The antenna loading coil was wound onto a length of perspex tube that I happened to have at just the right diameter. Paul (Museum Curator) machined a shallow spiral groove into it to keep the winding in place. (Pictures)
The coil tappings and capacitors are not yet connected as these are dependant upon the antenna characteristics and will be decided during commissioning.
That’s as far as it goes on the HF tuner until I can get back on-site.
The next issue is the Power supply and it is a beast! 3 Phase to supply 3KV HT, 6V @ 10A for heater, 220V screen, 24 VDC for control circuits. I can barely lift it so probably shouldn’t. However, I found the screen supply sub chassis and the HT timer PCB hanging on by their wires and a couple of yellowed noted from an exercise book noting which coloured wires go where. The timer PCB has seen some abuse around its 15V regulator and why that 10K power resistor has been bridged with a flimsy white wire remains to be seen. I should be able to test both these units on the bench before refitting them to the PSU. (have to add PSU pics in next post)
Further update to follow in due course.

Michael (GW7BBY/GB2MOP)
 

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Welcome back onsite, Mr. Oceanspan... lovely to get another update from you. How you manage to sort out all that gear is beyond me. I can't imagine having the skills and patience necessary to do any of that, even though I'm the most patient man I know! Your tech know-how astounds me, although it probably shouldn't. I compare what you're doing to the somewhat rudimentary skillset I managed to accrue during my time at sea. I guess it was the communication side I found the most interesting, that, and the fault-finding work, especially on radar, though with modified joy when 'put on the shake':

"Sparkie.. can you come and have a look at the radar..." (Always in the small hours of the morning when in the Channel and in thick fog).

Or the more usual: "Hands off c*cks, on with socks; rise and shine, do your thing for Sugar Line!!!" (All ports/windows pushed as wide open as possible, all overhead lights on and stereo/radio - if any - switched on, max volume). Sleep through that lot and you deserved a medal of some sort.

Towel wrapped around waist, stumbling up to the pitch dark wheelhouse: "O.K. I've looked at it, it's still there, now I'm going back to bed.."

'Just happened' to have an acrylic cylinder available? Just the right size? Now that is a coincidence. Looks like someone is looking after you and the museum. And someone who could make machine spiralling grooves to take the coil windings? That's stretching the old 'coincidence' bit a little. I'm always amazed, how things come together like this.

Keep well. The lockdown will force us all to take another look at what we do in our lives. Best of luck with the Museum and the radio gear.

Best rgds, as ever, Paul
 

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Discussion Starter · #23 ·
Thanks Paul, its good to hear your dulcet tones again! In way I'm sorry I missed all the fun of being at sea, maybe not so sure!
I've treasured that piece of acrylic tube for about 30 years and always knew it would be useful one day. I've still got about 18" of it left to go into a remote antenna coupling unit that I might actually finish if this lockdown lasts long enough.
Update to follow before too long.
Best regards - Michael.
 

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Mr. Oceanspan!

Halloo from across the seven seas, and hope all is well. I am waiting for your next installment about the good works at the new home of Marconi Marine and its wondrous and beautiful equipment(s). That piece of acrylic tube... has it found its next usage yet? So many questions. I'm like a kid: "Daddy, please, can you tell me why the anode coupling on the Oceanspan isn't .... well.. . coupling anymore?" "Daddy, please (tugging on shirt) ... when are you going to let me play with the tuning dials on the 'Oceanic'...?" "Daddy! You promised me that you'd get those lovely old Nixie tubes working again on the Apollo... can it still pick up Portisheadradio, Bergen and Barbados...?"


It's no good, I just can't stand it anymore, living here in isolation... I've got to have news of progress!! (When you have a minute, gov... when you've got a minute to lay down your 'scope probe and AVO, time to look out the window and think of us poor Marconiless souls living down at the bottom of the world when you pick up your cup of cold coffee... It'll be like opening my Chrimbo presents again, tearing the coloured paper and pretty bow off your next missive, desperate and overly eager to devour the contents.

Seriously? Must 'ave more, gov., must 'ave more.

Best regards for spring and the coming summer weather.

Paul
 

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Discussion Starter · #25 ·
Kelvin Hughes Progress

Hi Paul,

Things must be crook in the antipodes if you’re begging for posts. I was saving myself until I had a bit more to report. However, having been stung into action, I’ll do two posts, one on the Challenger and another, here, on the Kelvin Hughes. I mentioned PSU issues in a previous post, particularly the screen supply and start-up sequencer/Timer. When I tested the Screen supply on the bench it was only adjustable over 100 – 130VDC. It is supplied from a 250V tapping off the main transformer. One of the diodes in the rectifier bridge had failed, also one of the two 2N4240 was well below par, but not completely failed. Replacing the four rectifier diodes with a modern bridge rectifier and replacing both 2N4240s has fixed it. I now get the specified output of 200 – 250 VDC needed to set the nominal screen voltage at 230VDC. (Pic attached)
The timer/sequencer board operates at startup to delay application of HT until the heaters have been on for 3 minutes, or 1 minute standby to start. It had suffered severe overheating (Picture) at the left hand end where a poor little Zener had been struggling to drop 24+Volts to 15VDC. It also took out some of the tracks on the bottom of the board. I imagine some poor R/O bobbing around on the seven seas congratulating himself on replacing the Zener with the LM7815 regulator in the picture. The other Zener, a 5v one is also prone to overheating. I spent yesterday etching circuit boards for various projects including a small daughter PCB that picks up on the old Zener stud holes and uses a 7815 and a 7805 regulator with plenty of heatsinking. A benchtop lash-up established that all the logic circuits are working correctly but the relay just to the right of the burned section that is supposed to pull in the HT contactor is not making. It operates, but the contacts do not make. The heat has probably destroyed the tempering of the contact blades. I’ve found a supply of exact replacements from Poland and one is, hopefully, winging its way to me now.
The Kelvin Hughes synthesizers, one in the receiver and one in the transmitter, have a regulator board to provide + & -5V, +12 and +17VDC. I’ve got a handful of spares with faults. The lower voltages are OK, but the +17 rail seems to be a common failure. The regulator is an obscure IC: MC1461. They do turn up from time to time, but at very high price. Its expected to drop 37v to 17v, the current demand is not terribly high, but dropping 20Volts even for a couple of hundred milliamps still adds up to a few watts (4ish) to dissipate in an enclosed area with no heatsinking. So another of the little boards I’ve been etching is another daughter board to pick up on the MC1461 connections, but uses an LM317HV regulator with a decent heatsink. I’ll post a picture when I’ve assembled it.
The other PCBs include a revised over voltage clamp for the Marconi Oceanic. Oceanics seem to be prone to pass transistor failures: a single TO220 device on a heat sink to provide a lot of current at 5V for approx 100 TTL chips, display and various other functions. I’ve got the spare faulty Oceanic at home to experiment on. I’m planning to replace the TO220 device with a darlington TO3 device on a bigger heatsink. The TO3 device has much lower thermal resistance junction to case, bigger contact area with heatsink and better clamping force to heatsink. So fingers crossed! Just to make sure I’m adding a serious over-voltage clamp just to make sure.
The other circuit boards are a new Mic amp and mild speech processor for my home-built transceiver and an AM modulator. 35 years ago when I built this transceiver it was intended to be a multimode job but never got any further than SSB/CW. Now I’m getting involved with historic radio groups (VMARS in UK) AM would be useful so I can join in their nets.
Now go to the Challenger thread to read more!

All Best Regards – Michael.
 

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All I might need now is the wooden plaque: 'RADIO ROOM', on the door! Only partly joking, such is the severity of chronic reminiscing...


Paul/GRUA
Hi Paul - I know this is an old thread but a few years ago I too hankered after a "W/T OFFICE" sign for my reconstruction of a MIMCO stn. 'Span 7, Mercury/Elettra/Atalanta, Salvor, AKD, AA Rx - the lot!

So, I had a batch cast in bronze/brass and flogged them.

Then I got EVEN MORE requests for "RADIO ROOM" so I had several batches of those made up.
I have but ONE (1) left for sale! They are 15cm long by 5cm wide - solid.
They are polished to a gleaming shine, enough to satisfy even the nastiest Captain on his Sunday morning inspection!

Michael from MOF will tell you how nice they are as the Museum Shack has one of them.

PM or whatever they call it on here for details if you are interested.

=RGDS=BRUCE/GW4XXF=+
 
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