Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Split from the original offer thread: https://www.vintage-radio.net/forum/...d.php?t=159096

It's the same as an Atalanta except for the labelling. The ones on ships all seem to have been 2207C, with the bandspread scale pre-printed with the marine bands.
I assume this scale was supplied blank for the customer to mark up to their own requirements - it just has the lines, no numbers.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

As best I can determine, NS702 was the MWT designation. and 2207C Atalanta was the MIMCO designation. MWT literature and advertising did not seem to mention the Atalanta name. Possibly those units that MWT made for MIMCO carried both MWT and MIMCO nameplates.

2207E looks like a MIMCO designation. But without the HF marine bands bandspread facility, would it still have met the GPO requirements for a ship’s main receiver? As a “left-field” suggestion, might it have been used as a shipboard broadcast receiver, in which case the E suffix might mean the “entertainment” version. In the 1950s MIMCO used Dynatron receivers for this purpose, particularly the Dynatron T139/LF512 combination known as the MIMCO 2235A. But such Dynatron models only ran until c.1959-60, after which MIMCO would have needed other solutions. Pressing the Atalanta, perhaps modified, into such service may have been one pathway.


Cheers,

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Interesting I have some pictures and the knob on the front panel states push in for bandspread so I presume the facility is there.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Yes, the facility is there. The bandspread follows from the main tuning, so it can be labelled for whatever parts of the tuning ranges are of interest.

It looks like the Atalanta label and marine band scales were only used on the ones supplied as part of Marconi radio rooms on ships, and they all seem to be designated 2207C.

This advert promotes it as a general-purpose receiver, without the Atalanta badge:
https://www.vintage-radio.net/forum/...0&d=1382900750

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

The plot thickens!

There were also 2207B, 2207D and 2207D variants:

Attachment 188804

The 2207D was the 2207C when fitted with a muting circuit.

Attachment 188805

As the bandspread facility covering six marine HF bands was a “normally fitted” facility, it would appear that it was what might be called a “delete option”. That being so, perhaps the 2207E was a 2207C without the marine HF bandspread? In which case the 2207F might have been a 2207E with the added muting facility.

The above attachments are from a 2207C document dated 1967 November, so quite late in the Atalanta production run.


Cheers,

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

If the bandspread wasn't present why would the knob still be there also the calibrate wouldn't be as much use . And to meet the GPO specs the bandspread must be present . Without it to me a pointless receiver . There must be someone out there with the same model eventhough the seem pretty scarce just a thought .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

If the bandspread variable capacitor is there, the set will still do bandspread, but with a blank scale for the segments being spread, you get the slower tuning but you don't get a scale to tell you where you are.

As suggested earlier, this will work for a user who wants to use different bands to Marconi's usual marine bands, and is prepared to mark up his own bandspread scale with say an indelible pen based on pips from a crystal marker.

It's far from useless.. there is life outside the marine bands!

David

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Yes the variable capacitor is there David which is good I shall set about sorting the scale side of later . I am not familiar with the Atalanta .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

I seem to remember the band-spread only spreads the tuning scale, doesn't give fine tuning. No separate capacitor.

73

Colin.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

There is a small variable cap on the back of the panel that is behind the front panel with a pulley on it which when the bandspread knob is engaged moves it from what I can see .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Forget the last post that cap is for the fine tuning .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

It would appear that the bandspread facility is entirely mechanical in nature, not using a separate bandspread tuning capacitor:

Attachment 188854Attachment 188855

Thus on versions not factory-equipped with marine HF bandspread, the user would be free to choose six bandspread ranges as desired and to mark the scales accordingly.


Cheers,

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Sounds like the bandspread button drops the tuning gearbox into a lower gear and clutches the knob to the bandspread pointer as well.

Atalantas seem rather rare in private hands. There must have been plenty made, so I assume Marconi got most of them back through contracts and destroyed them to prevent a second-hand market developing.

David

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Yes, pushing and pulling the knob effects a gear change and so it is effectivly a slow-motion drive, which also engages the Eddystone-lookalike scale.
The bandspread scale plate is made of Traffolyte and can be removed by undoing four screws. It can either be engraved, or written up with a drawing pen, to suit the user's requirements.

The radio is very well made, and includes a bimetallic strip capacitor for oscillator temperature compensation.

The case and front panel are isolated from the receiver chassis. The AC mains supply, built into the back of the case, uses a transformer and solid state rectifiers to supply 110V unsmoothed DC for the HT and the heater chain. The smoothing capacitors are on the receiver chassis.

The mains filter is substantial, and the 2uF capacitors will *definitely* need replacing with modern Y types. For one thing it would trip any RCD in the mains supply - and for another, in the event of a poor earth connection the case would float at 110V AC with enough current available to deliver a very nasty shock.

I will post some pictures when I have found the correct micro USB lead for my phone...it must be here somewhere...

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Probably an Oxley Thermotrimmer.

If I remember right, the Tempatrimmer was a differential capacitor adjusting the proportions of a pair of fixed capacitors, one negative tempco, one positive, while the cheaper thermotrimmer used a bimetallic strip to move split 'stationary' plates that the rotor plates got a variable tempco. Could be somewhat vibration sensitive!

David

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

I had a Atalanta for a while - it didn't appear to have been wired for 110V at any stage, and I guess it was from an ex-BT coast station. It's true that Marconi usually destroyed the old kit which came back from their shipboard installations - which weren't actually sold to the shipowners, as I understand it. The Post Office / BT kit was purchased outright, though, and BT scrapped kit was sometimes sold for a nominal price on local arrangements.

The Atalanta was a very nice receiver, designed primarily for easy servicing. Lovely to work on. I'd still have it but for the sheer size. I think it was a bit bigger than an AR88, but it always seemed to be huge, and I just didn't have the space to accommodate it. It had to go, sadly.

The downloadable training manual on the Boatanchors Archive came from me - it's still got some of my pencilled notes...

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

I have two Atalantas but I have no idea about their history. I don't think that either has been to sea. One is a Marconi Marine and the other is MWT. Both continue to be very good and very reliable.

I started a thread some years ago on the topic, here:
https://www.vintage-radio.net/forum/...ad.php?t=99826

Compared to some of my vintage broadcast TV kit, it's quite a reasonable size and weight, but as ever with MWT products you do receive you money's worth in metal! As an ex-Marconi employee I can say that the old gag was that Marconi was really a metal-working company that did a bit of electronics, but that's not really a true analysis. They just made things 'properly' and items such as the Atalanta were made to last - unlike today's products.

Best regards,

Paul M

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Here is an early MWT advertisement for the NS702:

Attachment 189255

And here is a much later mention of the NS702 by the GPO as a representative marine receiver:

Attachment 189256

There does not seem to have been a lot of consistency when it came to the use of the mythological names. Atalanta appears to have been exclusive to Mimco. On the other hand, Hydrus and Argo were MWT names for receivers that had no Mimco versions. Apollo appears to have started as the Mimco name for the MWT N2050. It was not used by MWT in early literature for that model, but later advertising had it as N2050 (Apollo).


Cheers,

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

There was no 700 Kc/s calibration crystal in my Atalanta. I fitted a 1 meg crystal and a 1N4001 from SKG,2 to SKF,4. That gives me 1MHz markers and brings on the BFO in the "calibrate" position.
73, Andrew

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Good information it's definitely a well made Receiver .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Hi all. There are two rectifiers shown on the bottom right of the picture how do you test them ? I have done a diode test with a multimeter they don't read anything .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

I believe they are single plate Selenium rectifiers. There may be 7 of these in your receiver.

They are used for AGC, noise limiting and 'grid desensitising' functions.

The forward voltage drop may be about 5V and that would explain why you get no reading on the diode test. The reverse breakdown voltage may be as low as 20V.

If you desolder one end of each diode you could test them with a 9V PP3 battery wired in series with a 10kOhm resistor.

The AGC and noise limiter circuits may have been designed to make use of their characteristics.

If you replace them with a typical signal diode such as a 1N4148, you may alter the performance of the receiver.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Thanks for the info I had already ordered the 1N4148 diodes. I can't find any info on the rectifiers in the receiver would the cathode side be the one marked red on the rectifier or is that the anode ?

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

RED should be Cathode.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Thanks Hamish Boxer the receiver is working but the AGC is a bit hit and miss .

Re: Marconi NS702 / 2207E, SN 623 (Atlanta type) receiver
 

Just for general info on the diodes:

https://www.vintage-radio.net/forum/...4&d=1271872981

Lawrence.

Re: Marconi NS702 / 2207E, SN 623 (Atlanta type) receiver
 

Some info thanks Lawrence so the anode side is the disc side (red) .

Re: Marconi NS702 / 2207E, SN 623 (Atlanta type) receiver
 

Anode is the metal case.

Lawrence.

Re: Marconi NS702 / 2207E, SN 623 (Atlanta type) receiver
 

Cheers .

Re: Marconi NS702 / 2207E, SN 623 (Atlanta type) receiver
 

Hi all. Just to update on what's been done to the receiver the caps in the mains filter have been changed with y type capacitors and a new mains lead fitted . Quite a few 0.1uf capacitors were physically leaking and others measured high so i changed all of them on the various boards along with some others . The small value caps in the rf , oscillator, amp sections have not been touched . The caps on the output transformer and rf filter have been changed . Then checked the resistors again a fair few needed replacing . All the valve sockets had a good clean and the valves checked all okay except a low ECH 81 which I will replace . I had already changed some rectifier's . After this the receiver works quite well but not as it should the AGC was all over the place and the noise limiter didn't work so out came the AGC can I found it very fiddelly to remove but was careful on doing so . A couple of resistors were four fives times higher than than they should be so changed them also replaced two rectifiers with diodes and the refiitted the can . The set now works so much better the AGC is fine and the noise limiter works the rf gain is better as is the volume even with the small internal speaker i still have a few things to sort out but on the whole very happy with it .. The only problem I have is that band 6 is dead ! can anyone help with this as I am stumped cheers Chris .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Just to add the band switch has had a good clean .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Your "Band 6 dead" issue - can you confirm that the local oscillator is indeed oscillating on that band?

(Either use a 'scope, or - my preferred approach - use another receiver to listen for the local-oscillator; I prefer this method because sometimes the added capacitance of a scope-probe can be enough to stall a LO).

Another test-trick is to lift the grounded end of the LO grid-resistor and put a microammeter in there to measure the grid-current - this will also give you a feel for how the LO's 'perkiness' varies across the different bands/frequencies.

If the LO isn't oscillating, and 'band 6' is the highest frequency-range, first thing I'd do is swap the LO valve - a somewhat-tired valve may have enough gain at lower frequencies but not enough to sustain oscillation at the higher frequencies.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Hi Tanuki. There are 10 bands in total when you switch to cw on band six you can hear more but no signals .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Ah, that suggests the LO is working but you've got a gain-reduction issue in the front-end signal-frequency circuit of band-6.

One thing quick and easy to check is the continuity of the antenna-coupling winding on band 6; in the past I've seen receivers with this burned-out (after a lightning strike?) on one band, causing deafness.

If it's not that, then check the DC resistance of the various coil-windings on band-6 then compare the values with those for the windings on adjacent bands to see if they're similar. That your receiver works OK on other bands means the problem should be easier to identify than total-failure!

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Following further investigation I checked continuity from the band switch to L7 the aerial coil that's fine a 220k resistor was reading 290k so I changed that on the coil the 150pf cap read okay. Next L16 in RF1 the switch to the coil is fine another 220k was reading high 270k so changed that. The coils L25 and L35 are ok as are the band switch to the coil there is improvement but no signals .. Band six works with a LF rejector that is only used on band six could the issue be that ?.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Any chance you could post a snapshot showing the LF-rejector circuit? I'm familiar with the classic "IF wavetraps" - series- or parallel-tuned L/C combinations fitted in the antenna leads of some receivers to prevent breakthrough, but not with the specific circuit in your receiver.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

The 700kHz rejector is a parallel tuned job and it's in series with the primary of the RF coil that's connected to the anode of the 1st RF, it's connected between the "cold" end of the primary and HT, those two windings in series as a whole have a 680 ohm connected across the whole between the anode and HT, so far as I can make out.

Lawrence.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Hi Lawrence Is the RF coil L1 ?

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

L1 (plus C1) is the 700kHz rejector, I'm looking at the Atlanta 2207c schematic.

Lawrence.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Ah got it I will do further checks tomorrow eyes getting tired .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Checked The L1 coil that's fine C1 reads 0.003 uf the 680 ohm resistor is fine still the same .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Running out of ideas with this issue anyone have any more thoughts on it cheers Chris.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

I would first confirm that the local osc is working properly as has been suggested.

Lawrence.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Hi I presumed with the other nine bands working the oscillator was okay I have a scope but no leads only just bought it also no small radios only boat anchors so no room on the bench to put another on . Is it worth checking components around L35 in the oscillator ?.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Check the osc anode voltage, if that's ok try measuring the voltage on the oscillator's control grid, normally it should be a few volts -ve.

Remember that the first ECH81 is the mixer only, not the oscillator....

Lawrence.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

On band 6 the anode on V4 EF85 reads 42 volts . On L35 pin 1 reads - 1.9 volts . Pin 3 no volts. Pin 6 34 volts. Pin 5 34 volts .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Have you checked the anode voltage on V1, have you tried a sig gen for inputs or as a substitute osc, various things you can check, first is always the work you've already done.

Also the anode of the 2nd mixer is switched via the band change switch, is that voltage ok?

Lawrence.

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Hi , I don't have a sig gen I have checked and double checked my work so far it's fine I'm going no where now with it thanks for your help .

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

What frequency does Band 6 cover?

Re: Marconi NS702 / 2207E, SN 623 (Atalanta type) receiver
 

Medium wave .