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Old 28th Oct 2013, 7:15 pm   #21
GW3OQK Andrew
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Default Re: Marconi Atalanta - how good was it?

I dont know about their cost in the 1950/60s but one is on sale right now for only £599.99. Mostly they were rented out along with the Marconi radio station (Oceanspan etc) and operator like me who got £40 a month back then. Mine cost me £35 and the cost of making the psu. I'll be using it tonight on 3545.
Andrew
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Old 28th Oct 2013, 9:24 pm   #22
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Default Re: Marconi Atalanta - how good was it?

Me too Andrew! $43 per month and the Purser/Ch. Steward let you have $12 to spend!

OT - all the posts about Chelmsford are interesting. My late Father worked for MWT Hackbridge from 1938 to 1947 when he moved to New Street - I was 2yo! I well remember the kids Christmas Parties in the canteen. He would cycle every day from Braintree. I was a Marconi "Sparks" from 1964 to '69, Dad went back to Hackbridge about 1966, then to Plesseys in Poole in 1972.
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Old 14th Nov 2013, 11:22 pm   #23
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Default Re: Marconi Atalanta - how good was it?

Re marine SSB/ISB equipment in the time before SSB became mandatory at HF, the attached Marconi advertisement from 1965 might be illustrative. It refers to a naval transmitter. Presumably there was a corresponding receiver, or perhaps the HR24 was also sold for marine applications.

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Old 2nd Mar 2014, 2:47 pm   #24
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Default Re: Marconi Atalanta - how good was it?

Having just acquired an Atalanta, this got my surviving brain-cells interested enough to club together with this notion:

If a BFO were injected at 700kHz (calibrator?) instead of 85, then (I think) the fine tuning could be used to tune the IF either side of that, though one would miss the benefit of the product detector at the 2nd IF and wouldn't get the best from the filters. There is always the vacant space for V14 to play with but there aren't really any redundant controls to re-use.

As the beast was built, it's bearable for USB but the fixed BFO is in almost exactly the wrong place for LSB...

I wouldn't want to do anything irreversible, except maybe fit a modern IEC mains inlet filter.

And does anyone have a gash tuning gang cover for one of these, before I start metal-bashing? I guess the last owner maybe spent some time trying to locate the faulty micamold before he ran out of time himself... there but for the grace of God, etc.

Cheers,

Colin.
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Old 3rd Mar 2014, 1:09 am   #25
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Default Re: Marconi Atalanta - how good was it?

The Atalanta is an interesting case (oh, alright, to me anyway ) in that it uses RC filtering between RF stages and mixer (transformer aerial coupling) on its second-lowest frequency range, thus achieving the wide 4:1 span of 25-100kHz. (With LC filtering, a difficult 16:1 capacitance ratio would be necessary here). With unusually wide ranging general coverage receivers like this and "classical" circuit techniques, designers must have had something of a headache overcoming the daunting number of switched bands and array of tuning coils necessary, not to mention vanishingly low tuning span towards the LF end. Another approach is seen in the (also Marconi) CR300 where a span of ISTR 15-85kHz was achieved by low-pass filtering between RF and mixer. Obviously in both of the above cases, the IF offset in the LO circuit meant much lower frequency ratio, so conventional LC oscillator techniques were used here.

Queries have been raised in another recent thread as to why the Atalanta used the EF85 in both RF stages- I wonder if the lowish HT of (again ISTR!) 110V meant that the designer(s) felt that this high-slope valve would give the desired high-HF performance that (say) the typical EF93/6BA6 and stablemates would struggle to at low voltage?

PS. It's a slightly rough-and-ready (but entirely functional) solution but I've used offcuts of galvanized steel cable trunking to make tuning gang covers for receivers that lack them- they can be had in varying sizes and aspect. It's a shame that many sets didn't ever have them and a bigger shame when ones that did lose them. It's possible to find very narrow Terry clips that can be used to clip covers onto gang frames without drilling etc.- obviously care to avoid vane-fouling. Not sure if this is pertinent to the Atalanta but may give an idea.

Last edited by turretslug; 3rd Mar 2014 at 1:22 am. Reason: Supplement.
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Old 3rd Mar 2014, 3:27 am   #26
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Default Re: Marconi Atalanta - how good was it?

Hadn't thought of trunking lids - that might just be a goer. There's clearance for the vanes within the frame of the gang.

I've been delving behind the front panel tonight and feel the need to start another thread about the RF gain ganged pots!

I must say, I'm being favourably impressed by the Atalanta but haven't the room to drive it alongside anything else just at the moment for comparison purposes. This example hasn't been too hard used but I've had to bodge up a pot to get it working properly. Curiously enough, I picked up a CR300 at the same time but that's not likely to reach the bench for a year or so.
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Old 3rd Mar 2014, 11:10 am   #27
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Default Re: Marconi Atalanta - how good was it?

Colin, with my Atalanta the rf gain dual pot didnt work right and I discovered it was wired up wrongly, and it looked untouched since manufacture. RV2 inv log is at the back, RV3 log at front. If I had to change it I would have tried a single 5K linear!

The L/S area of my Atalanta had been cut out so I put a small variable cap (I think of about 50 pf) there with a long screened lead back to the BFO, and now it tunes +/- 85 kHz to resolve CW & USB/LSB. Looks quite good on my qrz page I think.

73 Andrew
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Old 3rd Mar 2014, 5:07 pm   #28
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Default Re: Marconi Atalanta - how good was it?

I think I'll roughly chart the resistor characteristics next time I take off the front panel. Perhaps ganged linear pots would be satisfactory - certainly easier to find! The original must have been expensive though. From that I would infer an importance that the maker must have justified.

Cheers,

Colin mm1aps
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Old 3rd Mar 2014, 5:31 pm   #29
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Default Re: Marconi Atalanta - how good was it?

Probably it was a standard part.

Log/antilog ganged pots were commonly used as stereo balance controls.

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Old 8th Mar 2014, 1:23 am   #30
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Default Re: Marconi Atalanta - how good was it?

Quote:
Originally Posted by turretslug View Post
Queries have been raised in another recent thread as to why the Atalanta used the EF85 in both RF stages- I wonder if the lowish HT of (again ISTR!) 110V meant that the designer(s) felt that this high-slope valve would give the desired high-HF performance that (say) the typical EF93/6BA6 and stablemates would struggle to at low voltage?
That is an interesting possibility. Data for the EF85 appears to be quoted only for the 250 V HT case, not for 100 V or even for 170 V (the latter a bit surprising). However, the UF85 (same except for its heater) data helps us here, as the 100 V, 170 V and 200 V cases were all presented. Slope with 100 V HT is 5 mA/V, as compared with 6 mA/V for the EF85 at 250 V. For the 6BA6, data is quoted at both 100 V and 250 V HT, I imagine because if nothing else, the 100 V numbers would have been pertinent for its 12BA6 counterpart. The slopes were respectively 4.3 and 4.4 mA/V for the 100 V and 250 V cases.

Another thought: I wonder if the EF85, being a “VHF”, was slightly quieter than regular “HF” valves at upper HF. There are other examples where Marconi used a Z77 (EF91) + W77 (EF92) combination in a two-stage RF amplifier, with the stated reason being the low equivalent noise resistance of the Z77. If the Atalanta designers wanted this benefit (from using a "VHF" valve) but also wanted a remote cutoff valve, then the EF85 would have been the logical – maybe the only – choice on a B7G or B9A base.

Quote:
Originally Posted by turretslug View Post
The Atalanta is an interesting case (oh, alright, to me anyway ) in that it uses RC filtering between RF stages and mixer (transformer aerial coupling) on its second-lowest frequency range, thus achieving the wide 4:1 span of 25-100kHz. (With LC filtering, a difficult 16:1 capacitance ratio would be necessary here). With unusually wide ranging general coverage receivers like this and "classical" circuit techniques, designers must have had something of a headache overcoming the daunting number of switched bands and array of tuning coils necessary, not to mention vanishingly low tuning span towards the LF end. Another approach is seen in the (also Marconi) CR300 where a span of ISTR 15-85kHz was achieved by low-pass filtering between RF and mixer. Obviously in both of the above cases, the IF offset in the LO circuit meant much lower frequency ratio, so conventional LC oscillator techniques were used here.
Agreed that it is an interesting receiver. The need to provide continuous coverage from around 15 kHz to around 30 MHz in a single receiver seemed to require some “gymnastics” as compared with “normal” general coverage techniques. The Atalanta had 10 bands and was single-conversion on some of the lower bands, but dual-conversion on the others. The IMR 54 also had 10 bands, but was single-conversion with a dual-frequency IF strip, 110 kHz (for some of the lower bands) and 465 kHz (elsewhere). The Redifon R50M had a similar IF approach, but provided the requisite coverage in 8 bands.

The arrival of upconversion receivers with wideband-capable front ends, which at a stroke dispensed with much of this tuning and IF complexity, must have been most welcome. But before that happened, some of the early solid-state marine receivers inherited the valve-era complexity. The Marconi Apollo had 10 bands, and I think – not sure about this – bandpass input tuning on all but the lowest two, which had single tuning. It was dual-conversion throughout, though. The Marconi Nebula (Eddystone EC958/5) also had 10 bands, with bandpass input tuning on all but the lowest two. It had a mix of single-, dual- and triple-conversion according to band, but to put this in perspective, some of that conversion complexity was associated with its use of a form of Wadley loop (which was effectively to the side of and not inclusive of the signal path) to obtain the desired stability.

The problems associated with VLF and LF coverage in conventional receivers is illustrated by the Eddystone 850 series, which used six bands to cover 10 kHz to 600 kHz, the lowest band being a mere 10 kHz wide, 10 to 20 kHz. These were upconversion, too, with an IF of 720 kHz. (I am not sure as to the origins of upconversion itself, but it could date from the first broadcast receiver with LW coverage to use a 465 kHz IF or thereabouts.)

Quote:
Originally Posted by Radio Wrangler View Post
Probably it was a standard part.

Log/antilog ganged pots were commonly used as stereo balance controls.
When was the Atalanta released? I’ve thought around 1956-57, but given that stereo amplifiers first appeared circa 1958, its possible use of a stock stereo component suggests that it might have been a bit later than that.

Cheers,
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Old 8th Mar 2014, 11:03 am   #31
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Default Re: Marconi Atalanta - how good was it?

Colin, do you have trouble with the pot?

The dual pot is 5K wirewound. I once repaired one which had burnt out the wire at one end of a track. I suppose the same wound track was used for both but fitted the opposite way round. There's a method to make a linear pot more log/antilog by connecting a res from centre to top or centre to bottom.
Andrew
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Old 8th Mar 2014, 1:22 pm   #32
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Default Re: Marconi Atalanta - how good was it?

The pot is working ok now with the soldered join but feels a bit rough and will give me trouble soon. I was planning to open it up again and sweat a bit of hard brass onto the wiper where it has been worn to a sharp edged groove by the track.

I have been looking various articles on simulating log and inverse log pots from linear ones.
Fortunately I possess a couple of decade resistance boxes to help out where my maths fails me!
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Old 8th Mar 2014, 2:27 pm   #33
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Default Re: Marconi Atalanta - how good was it?

As for how good was it, may I ask how good is it!

Is the Atalanta one of those models that is full of paper capacitors which are leakers these days?
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Old 8th Mar 2014, 8:24 pm   #34
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Default Re: Marconi Atalanta - how good was it?

As the thread starter, in answer to Steve in #33, all I can say is that I now have two of them and neither is a capacitor nightmare. My first one is used almost everyday and apart from a failed metal rectifier in the AGC system it has proven to be a star. The second one has not had a lot of hours, but there have been no problems - at least so far. I did worry about capacitors (I've changed far too many in vintage broadcast kit!), but there does not appear to be a 'global' problem with the Atalanta. Valve voltages are broadly within specification on both examples and I'm not expecting any issues in the near future. There's actually not that many 'suspect' types used in the design anyway. For its class, the stability is excellent.

If you're thinking of buying one, I would go ahead with confidence as there are no horrors inside and they are very well made - back in the days when Marconi was a metalworking company that did a bit of electronics! I jest, of course, but a feature of this era of Marconi kit is lots of heavy and beautifully hand-crafted metal. The machine shop at the New Street works was a marvel. It was full of highly skilled craftsmen, nearly all trained within the company's apprentice scheme. All gone, including the huge building which went last year.

Best regards,

Paul M

PS I've had no trouble with the RF gain pot - fingers crossed on that one!
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Old 10th Mar 2014, 10:48 am   #35
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Default Re: Marconi Atalanta - how good was it?

Thank you Paul M for your experiences. I asked because it had appeared to me reading about, that all the 'classic' valve SW receivers (non-domestic, mainly ex-Gov) require significant capacitor surgery. So it is heartening to know that at least one may not !
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Old 17th Mar 2014, 2:24 am   #36
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Default Re: Marconi Atalanta - how good was it?

One post moved to a new thread: https://www.vintage-radio.net/forum/...d.php?t=104551
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Old 30th Nov 2014, 10:47 am   #37
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Default

The Atlanta, indeed was very good marine main RX. for its time.
Unfortunately, the BFO, used to wonder a bit.
Used to be taking messages with one hand, and chasing up the Atlanta with the other.

Then the Apollo came out - smashing job. Oven on - all the time Xtal always stabilized.
If the Nixie tubes went out- then you had a major problem.
Then your reserve rx was the Marconi Sentinel.
OK for coastal work, but Long-range - forget it.

The Atlanta was a good main rx in its day.
Unfortunately the Apollo superseded it, with its Hi-Stab. capabilities,
and Nixie Tubes. Trained on Both - Worked with both.
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Old 29th Apr 2016, 9:43 am   #38
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Default Re: Marconi Atalanta - how good was it?

Quote:
Originally Posted by turretslug View Post
Queries have been raised in another recent thread as to why the Atalanta used the EF85 in both RF stages- I wonder if the lowish HT of (again ISTR!) 110V meant that the designer(s) felt that this high-slope valve would give the desired high-HF performance that (say) the typical EF93/6BA6 and stablemates would struggle to at low voltage?
Another thought on this – and admittedly it was a long time coming – is that the choice of the EF85 might have had something to do with the fact that the Atalanta was basically designed to operate on 110 volts DC supplies, and as a consequence had a 300 mA series heater chain. (Accessory power units were available to address AC supplies and 220 volts DC.)

Back when it was designed, if you wanted a variable-mu RF pentode of reasonable slope that was also specified for operating in 300 mA series heater, then the EF85 was about the only game in town. Like the EF80, it was one of those TV valves that was simultaneously a “P” valve and an “E” valve. On the other hand the 6BA6 probably had a more limited maximum heater-cathode voltage differential.

The Atlanta valve string did include one 200 mA valve (which thus required a heater shunt resistor) namely the W77 1st IF amplifier, but I imagine that this approach - heater shunts - would have been avoided as much as possible. One may then ask “why not another EF85”? Possibly this: the EF85, primarily intended for wideband applications, had been found wanting on the stability front in high-gain agc’d AM IF amplifiers in FM-AM receivers, and was largely superseded by the EF89 for this purpose. The adverse effects might have been worse with the 85 kHz very narrow-band IF of the Atalanta. So a conventional variable-mu pentode was required, and within the Osram range, that was the W77. The Atalanta probably predated the EF89 (which also had a 200 mA heater, like the EF41 before it). And MIMCO, which I think mostly leased out its receivers and did its own servicing, was probably happy to stay with valves from the British series.

Quote:
Originally Posted by PaulM View Post
I've been trawling back through the Marconi catalogues. Attached is a scan of the Atalanta's last appearance in 1968, the year before the 'absorption into the Borg' (the GEC takeover) of Marconi. Shorn of the 'MIMCo' badge on the top left-hand corner, it's just the plain and simple NS702 general purpose HF receiver. SSB was coming . . .
I wonder if the “NS702” designation was assigned by Marconi W/T for sales into other-than-MIMCO End-uses? As far as I know, Marconi W/T used the “NS” series (and also the “N” series) for its naval products.

MIMCO seemed to have used four-digit numbers for model identification, sometimes with a letter suffix. The one I have for the Atalanta, from the mid-1960s, is 2207C. I’d guess that there were preceding B and A variants. If we assume that the numbers were assigned on at least an approximately chronological basis, then the 2207 would predate the MIMCO 2232A, which was a cabin receiver, a rebadged Eddystone 670A, which was released in 1954. Somewhere I have seen the Atalanta described as a new model in a 1954 publication, so 1954 or maybe late 1953 seems about right. That would have made it quite an early user of the ECH81 valve (of which it had three), which evidently was chosen over the Osram X79.

Cheers,
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