Internal Fire - Museum of Power - Page 2 - Ships Nostalgia
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Internal Fire - Museum of Power

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  #26  
Old 14th September 2019, 22:49
Paul Braxton Paul Braxton is offline  
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Organisation: Merchant Navy
Department: Radio Officer
Active: 1969 - 1982
 
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Posts: 301
de GRUA...

Hello again, Mr. Oceanspan, Sir. Just wondering how things are on the 'ranch'. Desperate for an update on the Challenger and Oceanspan, and all things to do with that.

I got a couple of what look like brand new EF85's from a U.K. company for the Atalanta front end, but haven't got round to putting them in yet. Somehow find myself scared to do so, in case there's no improvement! How wimpish is that?

Best regards, Paul
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  #27  
Old 15th September 2019, 10:37
Michael Oceanspan Michael Oceanspan is offline
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Hi Paul,

You'll have to be patient! my wife and I are in the middle of a three week holiday in France (courtesy of my sister who lives in France). We'll be landing back at Poole on 22nd, then onwards to wonderful West Wales!

Really, you've nothing to loose by fitting the EF85s and maybe something to gain. Do you have a signal generator? I won't get round to realigning ours until the Winter shutdown (November 2019 to Easter 2020). Before that the HT supply needs sorting out. You probably know that the Atalanta has 110V LT - heaters in series via a varistor to limit inrush current and 110V HT. Ours has been modified by a previous owner for 240VAC mains operation by fitting an autotransformer: the 110VAC tapping goes to the filaments and also to a full wave silicon bridge rectifier consequently the HT is closer to 150VDC than 110VDC. From a purely electrical point of view it probably does no harm as all the capacitors are rated for 250V and the resistors should stand the extra few milliamps. However, from an RF and AF point of view I'm not so sure. The operating voltages; anode, screens and cathodes will be kept in proportion but elevated by nearly 50%. The set does have a tendancy to motor boat at maximum gain and stations are frequently accompanied by a hetrodyne. I'm hoping that sorting the HT and then re-alignment will resolve these issues.

As for the Challenger, I'm hoping to find a nice MRF393 or 392 waiting for me at the museum to replace the deceased BAL0000L10 in the driver section. The way will then be open to start checking the 4CX350s finals, one at a time. Then the fun begins!

Thanks for your interest - Michael.
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  #28  
Old 15th September 2019, 15:22
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GW3OQK GW3OQK is offline  
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Thanks Michael
It looks like adjusting L27 core might bring 8 MHz down to 7, (or 6 up to 7) but a tedious procedure without extender leads. Alternative add some fixed capacitors. You do have it working on 3.5 MHz don't you? Sounds like a winter job as you suggested
73,
Andrew
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  #29  
Old 15th September 2019, 16:35
Michael Oceanspan Michael Oceanspan is offline
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Hi Andrew,
Oceanspan works on 1.8, 3.5, 5 and 7MHz. 3.5 is very good, tuning on 5 and 7 is critical but do-able! Its debateable how useful the higher frequencies will be on AM, but it might make life easier for visiting CW operators who want to use the higher bands. Once the Challenger is up and running I might return to the Oceanspan in the Winter - unless Paul (curator) has some other winter projects to distract me!
Michael.
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  #30  
Old 16th September 2019, 07:39
Paul Braxton Paul Braxton is offline  
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Organisation: Merchant Navy
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Hi Mike. Hope you're enjoying your holidays.

Nope, I don't have a sig gen. In fact, I'm almost back to what was commonly available at sea, namely, an AVO8! (In fact, not as good as it was, as I've got no spares at all, not even suspect ones: 'used but good', was a common note to find written on valve boxes in those days).

My Atalanta has always been very well behaved indeed. I don't have your motorboating or whistling heterodyne problems at all, not even on max gain, and apart from the usual slight drift effects on listening to SSB, which is normal for that vintage set, there's been no hint of a problem, other than the occasional 'locking up' of the tuning control at one extreme end, when she sticks and won't come out of some internal detent. Easily fixed. I just talk to her nicely and she's right.

Even the dial cords are in exactly the right position and no trouble with the bandspread locking or use. Very accurate, in fact. I haven't measured the HT or LT lines, but that's interesting, what you say about the 110V. She can be a bit of a biter, the Atalanta; lots of opportunities to get a hefty belt if you're not careful. Especially on a rolling ship when you've got one hand clamped firmly around one of the chrome handles on the front panel, a gert big screwdriver in the other, forgetting that the inset screws for the knobs on 110V DC mains were live....

Your holiday in France will no doubt recharge you, ready to fit the part you mentioned in the big fella. Sounds like great fun, getting them up and running again.

Best of, as always, Paul

Last edited by Paul Braxton; 16th September 2019 at 07:42..
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  #31  
Old 16th September 2019, 08:15
Michael Oceanspan Michael Oceanspan is offline
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Hi Paul,

The Atalanta does bite! When it first arrived, I turned it on, twizzled the tuning knob as one does, found a station and just tuning in when the knob fell off. No worries, I thought, nearly got it, and took hold of the shaft to fine tune and you guessed it all the lights went out! Not mine - the RCD kicked in and saved the day, still got a healthy(?) belt though. A lesson well learned and not forgotten!

Michael.

Last edited by Michael Oceanspan; 16th September 2019 at 08:16.. Reason: Spelling
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  #32  
Old 16th September 2019, 13:02
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GW3OQK GW3OQK is offline  
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An isolation rather than autotransformer does have advantages Michael !

One of the first valves in the heater chain has a max heater to cathode voltage near 150v. My Atalanta had an intermittent heater wiring fault. My home made psu then rose from 110 to 160v off-load. The valve failed and burnt out the cathode resistor then the heater. I bypassed the faulty wiring.

With the Oceanspan on 7 mc/s it would be perfect for EU activity on a maritime activity day. Great to get it on 14 though.
73
Andrew
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  #33  
Old 16th September 2019, 14:30
Michael Oceanspan Michael Oceanspan is offline
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I'll bear that in mind Andrew. Looks like another good reason to sort out the PSU section.
Michael.
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  #34  
Old 2nd October 2019, 20:19
Michael Oceanspan Michael Oceanspan is offline
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Marconi Challenger

Paul, and others interested in the Challenger, can I refer you to the thread on the Marconi Challenger rather than repeat the story here?
In a nutshell, the replacement driver transistor arrived and is now OK. 4 new 4CX350s also arrived and am in the process of carefully fitting and setting them up. It's going well - so far!
73 Michael
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