Eddystone 358X

[G3PIJpeter]

I have just acquired an Eddystone 358X in original unmodified condition with a full set of coils, an AC PSU and a 6-volt dynamotor PSU. The only visible problem is C59 (4 mFd electrolytic) which has leaked all over the back panel rather like a decomposing dead mouse in the attic.
However, my first question is - when was it made? The serial number is FU1892 stamped onto a brass plate with a faint MD 218 rubber-stamped on beside it. I have searched the Web in vain for an Eddystone equivalent of the HRO manufacturing date decoder.
Photos attached for interest.
- Peter
G3PIJ

[M0FYA Andy]

Peter,
Have you tried the Eddystone User Group -
http://www.eddystoneusergroup.org.uk/
Andy

[G3PIJpeter]

Yes I have. I thought that I remembered seeing a serial number translation chart on that site a few years ago but I cannot locate it now - so I decided to give up and ask this group.
- Peter

[ms660]

I have one of these, I quite like them, mine has a factory fitted noise limiter (extra knob under the xtal knob)

The S/No: on mine is LX4212.

From what I can gather production figure was around 5,000 receivers, I can't remember for sure how but I seem to recollect the date of manufacture of mine was c 1946, the front panel escutcheons on mine are well de nickled and worn, It's missing the two of the lowest range coil packs the rest of the coil packs came with some their original cardboard holders, a bit tatty but still hold the coil packs ok.

Pics shown below, the receiver and two types of power supplies, the one with all the action on its front panel is the one that came with it, to date I have not fully identified this power supply, definitely made for Eddystone.

The other power supply is the type 390, according to the guff this is the one made for the 358.

ID of the first one mentioned...any ideas anyone...it's got the load resistor in it to simulate the normal sound output stage current draw when using it with the Eddystone 400 (selected by the power lead wiring to the plug) a variant of the 358 series.

Lawrence.

[Dave757]

Hi Peter

Although I uinderstand that the date letters are not 100 per cent
reliable, the Letters FU should be for June 1943 (the month I was born!)
Pre 1948 codes have the month first, A for January etc, followed by
the year letter, A - Z starting 1923, then repeating. From 1948, letters
are reversed.

Kind regards

Dave

[G3PIJpeter]

Originally Posted by Dave757

Although I understand that the date letters are not 100 per cent reliable, the Letters FU should be for June 1943

Thanks for the information Dave - I was born 2 years and 11 months later so my serial No. should start with EX - possibly followed by 0001.
Lawrence - my AC PSU looks exactly like yours, but it is currently fitted with a twin flex mains lead and adapter for plugging into a light socket. The rotary supply has the serial number CW which equates to March 1945 - see thumbnails attached.
My 358X also has what looks like a factory-fitted noise limiter, with a toggle switch and escutcheon on the front panel as shown on my first post. The wiring has obviously been added later and the noise limiting element is a small metal can with two wires and an earth lead mounted directly behind the toggle switch - possibly a couple of small metal rectifiers back-to-back?
- Peter

[ms660]

Peter, that's interesting, not seen one with a front panel toggle switch for the noise limiter before, the noise limiter in the receiver I have uses an EB34, it's mounted on top of it's own small chassis which in turn is mounted on top of the shallow sub chassis on which the sound output valve is mounted, the user control is a rotary knob, same size and style as the xtal filter knob with the same size escutcheon.

According to a online copy manual I have for the 358 the noise limiter valve (EB34) is shown as V8 in one of the schematics in the manual designated receiver type B34 which so far as I understand is an Admiralty designation.

There is a 358 up for auction as I write that is the same as the one I have.

Dave thanks for the S/No: info....I remember now how I originally figured out the year of manufacture.

Lawrence.

[russell_w_b]

I'm almost certain it was a wrecked 358X I came across inside the old WWII CH RADAR station blockhouse adjacent to the Forfar VHF transmitting station (located between Broughty Ferry and Forfar) back in '88. The pic of the front panel and semicircular dial looked identical to that in the pic in post #1.

It was a rack-mounted unit, and it was lying on the floor in the mud. It may still be there! I see no reason why such equipment should have been dumped there, in a quiet, out-of-the-way place, and I concluded, at the time, that it was part of the original station equipment.

[G3PIJpeter]

Originally Posted by pwdrive

... not seen one with a front panel toggle switch for the noise limiter before, the noise limiter in the receiver I have uses an EB34, it's mounted on top of it's own small chassis ...

The only thing that makes me claim the noise limiter in my 358X is 'official' is that the toggle switch has a '358-style' escutcheon around it. An EB34 is not present - the actual ANL element (1.5" tall x 1" wide x 0.5" thick) is connected to the toggle switch as can just about be seen in the thumbnails. The black and yellow connecting leads terminate around the output valve - I shall trace exactly where later. The lead to the top of the element is simply an earth strap.
If anything, the mystery deepens.
- Peter

P.S. Does the selectivity control go 'click' when turned on/off? The switch inside the IF box seems to be a wafer type with the detent ball missing - but it's difficult to see at all clearly.

[HamishBoxer]

Mine does.

[G3PIJpeter]

Quick update:
I've just applied filament volts and everything lights up - including the inside of what I have referred to above as "the ANL element" - the little metal box next the the rear of the ANL toggle switch. It's too small to house an EB34 so I reckon there are a couple of VR92/EA50s in there and what I thought was an earth strap is, in fact, a lead to the anodes.
The HT line reads 27 kOhms with the filaments cold but I switched off the HT when the PSU milliammeter went above 150 Ma. More work needs to be done. I think I shall have to live with the non-clicking selectivity switch for the time being.
- Peter

[ms660]

The selectivity switch on mine does not click either eg: no detent.

One picture shows the EB34 atop the ANL sub chassis which is mounted to the right of the sound output valve, you can see how close the xtal filters selection cable is to the EB34.

The other two pictures are of some of the cardboard containers that the coil packs came in, the cut outs in the false bottom are for the three blocks of the connector pins on the bottom of the coil packs.

The ANL arrangement in Peter's receiver looks original to me also.

Lawrence.

[G3PIJpeter]

Originally Posted by pwdrive

The selectivity switch on mine does not click either i.e. no detent. ... The other two pictures are of some of the cardboard containers that the coil packs came in, the cut outs in the false bottom are for the three blocks of the connector pins on the bottom of the coil packs.

Good to know that the lack of click does not indicate that some unusual rotting process or whatever has taken place inside the filter box.

I suspect that my 358X had a military background for its entire life because it was sourced from a recent MOD auction and the coils came in two cardboard ammunition boxes labelled 'Medium Velocity'.

Closer inspection is revealing that almost all of the original capacitors are leaky, variously in both senses of the word. The resistors look very much 1930s in style despite the 1944 date of manufacture. I have decided that I shall do a full replacement of all passive components, as Jerry O'Hara's account at http://eddystoneusergroup.org.uk/Res...l%20S.358X.pdf I did a similar job on an HRO/R106 a couple of years ago and the 358 is similarly get-at-able. The fabric-covered wire in the main looms looks OK.

- Peter

[G3PIJpeter]

Originally Posted by pwdrive

According to a online copy manual I have for the 358 the noise limiter valve (EB34) is shown as V8 in one of the schematics in the manual designated receiver type B34 which so far as I understand is an Admiralty designation.

Lawrence
The rebuild is coming on apace and I am now wanting to refit the noise limiter. However, the circuit that I traced of the single diode setup originally fitted does not make any sense. I have tried to find the EB34 circuit on the Web to which you refer but with no luck. Could you please point me in the right direction or supply a sketch of the noise limiter part of the B34 manual you have.
Many thanks - Peter

[G3PIJpeter]

To complete the story, here is the circuit of the single diode noise limiter that I finally found earlier this evening. The download from BAMA includes the Navy B34 circuit which contains this NL, unlike the standard 358X.
- Peter

[ms660]

Peter, my apologies for not responding to your request in post#14 as I have only just come across it.

Good luck.

Lawrence.

[G3PIJpeter]

Lawrence

Your 358X noise limiter (post above of 26 May) contains an EB34 which is a dual diode. The circuit I found (dated 1949) uses a single diode which, in my 358X is a VR92 miniature diode.

Does your NL consist of a negative/positive peak clipper as is more usual? Mine seems to ride on the AVC to set the clipping level for positive peaks (but then, I suppose impulse noise sits on the positive side only of an AF signal.

It seems to me that the fitting of an ANL to this receiver was an afterthought and possibly only to the Navy B34 product - which also had twin 600-ohm audio outputs rather than the usual different impedances for headphones or speaker.

- Peter

P.S. I am pleased to see that this topic has promoted me to pentode status!

[ms660]

Peter, the schematic in your post#15 is the same as the schematic I have.

Unfortunately I can't get access to the underneath of my receiver to work out what's what at the moment, however a few minutes ago I removed the EB34 and did some quick resistance checks from the topside of the valve socket, pins 5 & 8 (a1 & k1) are shorted out when the the ANL knob is turned to the off position, with the knob in the same position there is no resistance reading between pins 3 & 4 (a2 & k2)

I have a feeling that only one half of EB34 is actually used, if that is the case then the noise limiter (schematic wise) in my receiver is as per the schematic you posted.

Lawrence.

[G3PIJpeter]

Originally Posted by pwdrive

I have a feeling that only one half of EB34 is actually used, if that is the case then the noise limiter (schematic wise) in my receiver is as per the schematic you posted.

Thanks for the research Lawrence. It seems fairly conclusive that we both have the same circuit but with different hardware, so I shall stop chasing after something (a double-diode limiter) that does not exist.

I shall have to wait until the rewiring is complete before experiencing just how effective this limiter is (or is not) with impulse noise. I remember from my 1960s SWL days that every time a car came down the road, the RX audio was filled with a harsh popping sound in time with the sparking plugs. Not such a problem these days.

Advice for 75A4 owners is to bypass the ANL with a capacitor so it may well be that the need for a limiter/clipper is long past.

- Peter

[ms660]

Last time I fired the receiver up the noise limiter did seem to work ok considering what's in it, not as good as the Lamb limiter though, but that's to be expected.

Lawrence.