Internal Fire - Museum of Power

Andrew ,
The 1950's Radio room has been functional since last year and since the beginning of this year all Transmitter (Oceanspan) and receiver (Atalanta and Mercury) functions have been properly integrated to provide AM and full break-in CW. At present we can use 1.8, 3.5 MHZ easily, 5MHZ and & 7MHZ at a push. I frequently use it on VMARS' Saturday morning AM net on 3.615MHz. Last Saturday morning I was on with good AM contacts throughout the UK. (I am rubbish at CW)
We put in a good showing for Museums On the Air and also Marconi Day in April. (Oceanspan story do***ented in Practical Wireless April 2017 and April 2018)
In addition to the Rohde and Swartz 2100 that any visiting amateur can use, the 1950's radio room can also be used, but under supervision. (Not that many Amateurs are used to separate RX and TX, or tuning up large Valve transmitters!). If anyone does want to use the 1950s Radio Room, give me a PM or email via GB2MOP website and I'll try and be there to meet you. The only day I am committed to the Museum is Wednesday, we don't live far away and I'm often there on unpredictable days as well!!
The 1980s Radio Room from the "Pride of Calais" has working receivers, autokey and AutoAlarm. After a frustrating voyage of discovery the 1.5KW Challenger is within an ace of working (awaiting parts). See thread on Challenger on this forum - any info on Challenger or Station wiring would be gratefully received!

Best Wishes - Michael (GB2MOP/GW7BBY)

GB2MOP de GRUA... G'day Michael Oceanspan again, from the wet, dark climes of New Zealand.

So nice to see a photo of your '50's radio room setup at last, complete with our friend, the Oceanspan. It brought back a few, looking at that. Now I remember a few details I'd forgotten, including the large indicator lamps on the front panel. May I ask, what is the little red panel over a couple of switches on the front right bottom side? Think one of those must be the HT switch, but what does it say in the wording on the red?

Nice to see a layout like that again, though I don't know about '50's. I was used to seeing that in the '70's! Never had an Atalanta as well as a Mercury, or Elettra (Electra?), which would have been so much better than the more usual Alert RX, which, in my opinion was worse than useless, a veritable waste of space, in fact. I'll have to send a photo in of my tiny museum piece, which is so small due to the fact that it's just in a back room of our house and I can't get my hands on any more equipment.

73's for now. Paul

First of all Paul,

Glad you like the set up, the Oceanspan acquits itself very well. Now that its teething problems have been sorted out, mainly poor modulation, I get very good reports. I’ve been re-routing the antennas feeders via an antenna switch in anticipation of the Challenger coming on-line. As the feed from the Oceanspan is now in Coax, the length of the radiating component (Was inverted “L” direct to top of Oceanspan) is shortened, the antenna current has increased considerably. Still getting a good signal into Hack Green at 1530Hrs, be interesting to see how it goes earlier in the day.

I’ve attached a picture of the panel you mentioned. As you will see it is to select “Quick Heat” or Normal, Autokey or Manual Key. Our Oceanspan was a VIIE – an Oceanspan modified by Marconi as an Emergency transmitter when they found they had plenty of Oceanspans on hand in the early ‘60s and Oceanspans were being outclassed by more powerful SSB transmitters. I’ve reversed the modifications to revert it to Main Transmitter status. ( I don't know if existing Oceanspans were converted to VIIE, perhaps when a ship's equipment was upgraded?)

An Electra would be nice to go with the Mercury. However the Atalanta is a very nice receiver, but in need of realignment following replacement of nearly all its capacitors – a job for a quiet day with no visitors!

Now Andrew – well spotted! Yes DDS based vfo driven by Arduino (picture attached) opens the way to any Amateur band except that I can’t tune the Oceanspan driver stage higher than 7MHz. Problem is that 14MHz falls in the gap between 12 and 16MHz. The tuning slugs are underneath the transmitter unit, as soon as the transmitter is pulled forward off the Z contacts it can’t be powered so live working without some elaborate jiggery-pokery is ruled out. I might have another go at it during the winter shutdown: a) I can shift the vfo output to whatever multiple of 14MHZ the driver is expecting, b) it could be done “cold” with a signal generator or c) if I’m bored - some dangerous jiggery-pokery!

The unit below the VFO in the picture is a PSU to provide 650VDC for the Oceanspan and various HTs for the other equipment in the bay. Optionally you can have the Rotary converter running in the Oceanspan if you want the full R/O experience!

Sidetone? Now there’s a question, sidetone is present although I haven’t specifically wired it in and there is no obvious contact on the Oceanspan. Now you’ve made me think about it, I’m probably hearing it by virtue of the signal being strong enough to breakthrough the receiver on de-sense.

The Lodestone DF, probably works. I’ve not given it a lot of attention, but it is nice and clean inside. I’m thinking of feeding it with an Arduino generated nominal 500kHz signal with the ability to differentiate it between P & S, F & A antenna feeds. Of course if anyone’s got a Bellini-Tosi DF antenna kicking around……

Best Wishes - Michael (GB2MOP/GW7BBY)

Old Capacitors

Hi Paul,
All electrolytic and waxed paper capacitors become suspect after 40 or more years, more so if the equipment has been laid up unused for a long period. High value resistors generally tend to go high.

When it first arrived the Atalanta worked after a fashion, it would motor-boat (LF oscillation) if the RF gain was turned up too much; when a signal was tuned in it would be accompanied by a strong hetrodyne. There were other spurii to be heard as the tuning was changed.

There were a couple of burned out resistors and the RF gain control was faulty - that was tricky, it is a dual gang pot: one gang is Log, the other is anti-log.

After replacing the capacitors, and resistors mentioned above, it is greatly improved. The tuning is 500KHz out according to the dial in places and it has some quiet spots. It does some quite complex frequency changing so I'm looking forward to a day with Signal Generator and 'scope to sort it out.

The Mercury hardly worked at all when received by us, a couple of capacitors had actually exploded in it leaving shards of tin foil everywhere and it had a fair share of burnt out resistors. After replacing the all paper and electrolytic capacitors and re-alignment it is now a very nice receiver.

One more thing: I'd always believed mica capacitors to be reliable. However, the Mercury stopped working about two months ago, the fault was traced to lack of HT at the 1st Local Oscillator valve. The HT was fed from the HT rail by a 10K resistor (from memory) and bypassed to chassis by a 0.1 or 0.01uF mica capacitor. That capacitor had gone short and thus robbed the valve of its HT. So now I suspect all capacitors, though in fairness mica is still generally more reliable.

Incidentally, I do replace with modern components but photograph before and after so that all changes are do***ented. Originality is a subject often raised. You can get new/old stock TCC etc capacitors at a price but at over 30 years old are they any better than the ones you are removing? I know some people hollow out the old capacitors and fit modern ones inside. You have to weigh up how much originality means to you. The museum maintains a policy of keeping everything working - engines and radios. By fitting modern components such as capacitors and resistors where needed, the equipment can be kept in reliable safe working order without detracting from its appearance, feel and performance.

If your Atalanta is going deaf above 7MHz, can you get the front end valves checked or substitute known good ones before delving deeper?

Best Wishes - Michael.

Hello Michael,
about the sidetone, from the transmitter it connects to the Atalanta on terminal 21. See page 75/76. Excuse me if I say it was needed because we were not listening to our own transmission. Typical would be tx on 12622, rx 13125. Do you key your DDS so the spacer wave isn't heard?

On my Atalanta I have a pot across the desensitising back-contact so I can adjust the muted level to hear my own transmission. I only use a straight key, with back contact desensitising all my vintage shack receivers, via 1N4001s.

It's many years since I worked on an Oceanspan. The temptation to adjust cores or clip out a fixed capacitor on the 12 mc/s range multipliers would be great. I'd like to see a scan of that circuit. I can't remember it but I suppose we had a Z-contact extension cable.

At the top of my garden I have what looks like a Belini Tosi loop. It's two three metre white plastic pipes with wire inside. The pipes go via glands into a JB, where there's an amp and then to shack via Cat6 cable. Without the amp it could go straight into a Lodestone!.

73 Andrew

GB2MOP DE GRUA...

Back to you, Mr. Oceanspan, and that's a very interesting post of yours, the one about the capacitors, etc. Sounds like I was pretty lucky. My Atalanta was working from day one; all I had to do was remove the large capacitors across the filter at the mains I/P to get it to run, then I was pleasantly surprised (and in reminiscence mode) to hear it working on all bands with a little bit of wire going out the window to the rotating clothesline. Haven't got access to any replacement EF85's at the moment, but will get back to trying that out when I get time.

I did always like the Atalanta. It had a sort of familiar solidity about it, a bit of comfort in an old friend, sitting there waiting to connect you with the world, reliably and constantly. Once the Apollo came along I was, however, hooked on that, never giving the poor old Atalanta another thought in the face of such sophisticated, ultra-modern glamour. How fickle. Good job it has forgiven me for such an unforgiveable lapse and goes on working, dried out caps and all... Also have to admit to forgetting all about that other old friend, the Oceanspan, once the Commandant and Conqueror marched in and took over. But it's been nice, looking at all your posts, and particularly the photo of you in front of the 'Span.

From memory, when I was at college in the late '60's, we had a couple of Oceanspans, one in one of the lecture classrooms and another in the 'Cabin', where we got our hands dirty on the thing. The classroom one was always used for practice in simple tuning procedures, etc., and was otherwise unused (as far as I know). Just sat there on a bench at the front, idle and silent for the most part, waiting for the next, just out of school guinea pig to come up and and make a complete ass of themselves in front of all their mates:

"Right, Mr. Braxton. Would you like to come up here and show everybody how to tune the Oceanspan on 12546 MHz please. NO, NO, boyo; you always tune for a dip!"

Well at least it gave everybody a good laugh, gave them all a break from Mr. Kirchoff's Laws, Fleming's Left Hand Rule and the workings of Colpitts oscillator circuits.... Happy days.

Regards, Paul