Eddystone 358X Receiver

I bought this old receiver at an on-line auction without inspecting it and as only a general view (above) was shown I had no idea of its originality. I don't believe the auctioneers ever looked inside because it's been fitted with an internal power supply complete with lead and 13-Amp plug. You can see this below and you'll notice the mains lead is a bit odd having an extra safety earth wire (in black). No electrical safety label and mains lead intact.

You'll also notice the "modern" valves which look to be expertly added (except maybe the large one over on the left which is fitted in what appears to be an early 1930s holder). I wonder if that's a Q-multiplier tucked away in the corner... No it's the BFO?

Above, you can see the new mains power supply and voltage regulator top left, plug-in coil sockets left centre and the IF transformers on the right. The flexible cable connects the front panel knob to the crystal filter and at the bottom right the audio stages. The BFO is that small metal case mounted on the front panel, presumably fitted here to provide a nice panel layout? That crystal filter control plus the HT switch are clearly afterthoughts as their positions look a bit odd.

The identification label fitted on the metal screen is shown here and correctly shows 358X together with the serial number GW3357.

This code "GW" indicates the manufacturing date was JULY 1945

This is the label on the coil box showing Royal Navy codes "Ad. Patt. W4991 for Ad Patt. W4989A Receiver B34".

The 358X was known by B34 in the Royal Navy.

It looks like the coilbox and receiver were not original mates or later introduced?

The label on the receiver outer steel case is missing.

As you can see the coil box is labelled "2364" so I looked at its contents and found all the coils except Range F had this same number. Range J had the number "2017" so was not part of the original set being apparently earlier.

The receiver uses a set of ten plug in coils, an example of which is shown here.

When the receiver was designed (I believe in 1940) there were three options available for RF coils. The simplest, used for example, in the AR88 and R107, which have a wavechange switch. A drum such as that in the DST100 and the R206 or, as here, a set of plug in coils like the HRO.

Each method has advantages and disadvantages. If, for example one is told to switch off the receiver before changing coils, stability and drift will be compromised. The advantages are much easier production line assembly and alignment.

To minimise drift the front panel carries an HT switch so the valve heaters are left lit when swapping coils.

The ten wavebands are listed below

RANGE	A	B	C	D	E	F	G	H	I	J
MIN_FREQ_KHz	22000	9000	4500	2100	1250	600	300	150	90	40
MAX_FREQ_KHz	31000	22000	9000	4500	2100	1250	600	300	150	90

A common amateur practice, when commissioning any government surplus equipment back in the 1950s and 60s, was modifications to improve performance, commonly following advice in a monthly periodical such as Practical Wireless. This advice was usually to substitute modern, higher performance valves and improve usability such as adding a built-in mains power supply.

I checked and found none of the original line-up of octal valves were in place as these were all swapped from the original set as follows...

	V1	V2	V3	V4	V5	V6	V7	V8	V9
ORIGINAL	EF39	ECH35	EF39	EF39	EBC33	EF39	EL32	NA	NA
NEW	EF183	ECH81	EF89	EF89	EABC80	6BE6	6BW6	EZ80	S130

How to deal with the set? My plan is to leave everything electrical just as the last owner left it except for checking the condition of the parts. I'll not be removing the power supply, putting back octal valves or removing anything not original. However, the front panel will be detached, stripped and finished in a suitable paint. Hopefully the labelled disks, or control escutcheons, will clean up. The outer case will also be stripped and repainted. The few blemishes on the chassis will be treated with a rust remover.

Here's the circuit diagram of the Eddystone 358X

click to see a larger picture

For some reason the dial is calibrated for only four ranges (B, C, D & E) with the other six relying on curves linked to the 0-100 logging scale. One reason is that at least in some examples, the dial calibration may have been outside the specified accuracy of the receiver, bearing in mind that in practice the plug-in coil packs may be switched between receivers. An alternative more pragmatic view is that to display ten wavebands plus a logging scale would result in an overcrowded dial making it difficult to read. In the six cases where the dial is uncalibrated the set has much the same inconvenience as the HRO, although in fact in the normal usage of receivers during WW2 the resettability was more important than accurate frequency indication, hence the provision of the vernier logging disk.

A receiver whose dial carries lots of wavebands is the DST100 and reading its dial is not easy although it has only a mere seven

As is customary here the first task will be to check that it's worth proceeding. I believe it will be OK as I twiddled the tuning control and it felt really good. Nothing appears to be missing and I guess any really bad components have been changed. Looking under the chassis might reveal if there are any clues as to when the major work took place as being a valve conversion the new parts will now be getting on in years. The best I could do was an HT electrolytic marked "1955", but as most other "new" components date from before 1960 my guess is the conversion took place around 1960.

Comparing a typical unmodified set (above) and mine (below). The RF amplifier and mixer are on the left with the IF and audio stages on the right.

The major new parts are the mains transformer mounted bottom left above chassis, the HT choke centre of chassis rear and the reservoir plus smoothing condensers (adjacent to the choke and chassis front). That fat green ballast resistor at first sight might have been the load for the S130 voltage regulator valve with the early B4 base but I noticed one end wasn't connected and might have been swapped for that smaller adjacent green wirewound resistor? The parts in the bottom left area are the EZ80 rectifier with associated tagstrip carrying mains transformer connections.

Below.. the control escutcheons looked beyond redemption but cleaned up well. The finish looks like nickel plate and prolonged exposure to damp air looks like copper plating had leached through. After a lot of rubbing the tarnished surface cleaned off to expose a coppery finish which cleaned off after a lot more rubbing with Brasso.

Above.. This small panel was awkward to detach because it was secured by a pair of 6BA screws with almost inaccessible nuts. It could have been worse as it should have been secured by four screws as you can see.

It's vital to use snug-fitting screwdrivers in all fittings, knobs, circular and other parts as over the years the screws will have bedded in.

The last restorer had been a bit premature and fitted the escutcheons before the black paint had hardened sticking them firmly to the front panel.

As I cleaned up these plates they went from horribly tarnished, through to a pure copper colour then finally to this silvery finish.

I tried various proprietary cleaners but spit with its enzymes is probably best, finishing off with Brasso. In fact spit and aluminium foil was by far the best option just as it used to be perfect for cleaning bike handlebars.

More cleaned up labels. I couldn't remove the label under the crystal filter switch at this point and I didn't want to damage the main tuning knob whose securing screws wouldn't budge.

I'm planning to strip the front panel with these left in place and masking the dial glass etc.

Here's the meter (not original?). Part of the very fragile pointer went missing and I'm not sure where the pointer should be set in its rest position. Just looked on-line and it seems the lefthand picture shows the correct position.

I scanned the original corroded dial at 600dpi then Photoshopped the result to leave the lettering etc in place. The paper facsimile was then glued to the rear of the brass dial. The adjusting screw was completely seized so further pointer adjustment means pulling out the movement.

I'll redo the paper overlay and add new lettering to replace "set carrier" plus a green centre area to match the original sets meter. The centre area is supposed to indicate good valve anode currents.

I found a picture of a 358X that showed the original meter and I've reproduced its salient points although changing the centre zone from black to green. I've left the other meter details to identify the movement etc.

I generally emphasise PhotoShop colours because when printed the colours are paler than shown due to the printer settings.

As the meter was a centre zero type and with a fairly fragile pointer I had some trouble backing it down to the zero mark. It was only when reassembling the front panel I realised that the valve test switch had been replaced with a pot and, as this was connected to the meter, I twigged the set now had an S-meter.

I'll decide later how to resolve this.

The front panel ready for applying paint stripper. The stuff I'm using is a bit puzzling because the front label says it uses "Methylene Chloride" but the label on the back declares "Non Methylene Chloride" so I'm none the wiser. It's worked admirably in the past so cross fingers...

As I peeled off the unsightly black paint the original grey crinkle was revealed. In fact it took three coats of stripper to get down bare metal and I then decided that repainting it in-situ would be too risky as the panel needed to be scrupulously clean for a good paint finish. The remaining problems were the main tuning knob and the crystal filter knob. I managed to free the centre knob. One screw gave in to turning but the second needed tightening first. There was a crack and the screw was suddenly loose so the knob lifted off. The crystal filter knob plastic had already broken into two (but gluable) and the centre brass bush wasn't going to budge so I levered it off little by little. Then the panel bush needed to be unscrewed to free the escutcheon.

After stripping the thick black paint lots of screws became visible. Removing four large ones from their nuts freed the panel and then unscrewing four tiny screws freed the dial assembly (see details later). Finally the BFO chassis was detached after removing its pair of 4BA securing screws. Now I can detach the tuning spindle bush, remove remaining paint, smooth with wet emery cloth, wash and respray.

Before and after. Nothing like the original Eddystone finish but more presentable than the black version.

The chassis (with rather cluttered surroundings ) is shown below.

The dial assembly is secured to the front panel by four short countersunk 6BA screws allowing it to rest on the flywheel when the chassis is resting on its rear edge.

The slow motion drive remains fixed to the chassis.

The glass, which is 5mm thick, is held in place by a set of metal brackets.

The dial pointer is detached after turning the tuning knob fully anticlockwise to maintain tuning. This then allows the dial to be lifted clear.

Note that the numbering is deeply engraved so there's no problem in cleaning it.

The dial lamps must have been removed by the last owner.

Once the front panel paint was beginning to harden I began reassembly. The dial assembly was a puzzle initially until I realised the only way to fit it was to mount the four posts and glass securing brackets to the front panel then fit the dial plate after the panel had been secured in place.

The procedure is as follows:

Fit all four short threaded posts to the front panel. To help with this each post has a 6BA threaded hole through the sides. Thread a long 6BA screw through the hole and use this to position the posts. Before fitting each post to he rear of the front panel you need to add a glass dial clamp. Initially leave each upper post slightly slack but tighten the lower posts ensuring the glass clamps are in the correct horizontal position to accept the dial glass.

Now position the dial plate to align with the top left mounting post, thread a 6BA screw and washer to loosely secure the dial plate left top corner. Now (temporarily) loosely secure the top right of the dial plate similarly. Note the lower 6BA screws should have hex heads as screwdriver access is limited. Fix the lower part of the dial plate with their hex screws.

Fit the dial pointer in the same position as it was detached earlier. If the tuning has been disturbed, tune so that the tuning condenser is fully unmeshed then secure the pointer through the hole in the dial plate to the gearbox shaft and tighten the pointer at "100" on the logging scale.

Remove the upper right post from the dial plate and front panel. Use a long 6BA screw to help with this as previously.

Now carefully slide the glass into place so the lower left edge fits in its bracket. This can be helped by opening the clamp with a long thin screwdriver if the clamp is too tight. Locate the upper left clamp and slide the glass across so it simultaneously engages with the left lower, left upper and lower right clamps.

The glass should now be secured by three clamps. Add the upper right post and clamp helped again by a long 6BA screw fitted in the side of the post. Tighten the post to the front panel with the glass clamp in place (again helped by the long 6BA screw). Finally check the glass is roughly central and tighten the 6BA screws securing the dial plate. You might need to tighten the pair of lower hex screws with a 6BA spanner. Note that the dial lamp cable clamps may be required under the hex screws.

Above, the receiver panel reassembled. I had to drill out one of the broken knob grubscrews, tap it and make a new screw. By now I'm getting familiar with the thing and I've noticed that the tone control is a yaxley switch (not the R40 pot) and the control below the meter isn't a rotary switch , but a wirewound potentiometer. The next step is to check for shorts and if OK, plug in a loudspeaker and apply power. I'll leave the meter disconnected as the movement is only 250uA.

Click to find out what happened when I powered up the receiver..

Eddystone 358X Receiver

Here's the circuit diagram of the Eddystone 358X

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