R1475 or Type 88 Receiver

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This may well be my next major project. Shall I build a guard unit to plug into the front panel in the space occupied by the dummy unit with the black front or not? If I decide to do this I'll need to add back missing switches etc.

I'll also need to find or make a suitable power supply (for mains ue) as this is a "Type 360" in a separate box. See below..

Click the circuit to see it full size

Strangely this receiver uses a form of modular construction as does my latest project getting my Plessey PR155G working properly.

What can I do to this old radio to improve its looks? The front panel looks scruffy with peeling paint at the magic eye panel, a matt black finish to the old guard channel plug-in and lots of holes. I did look at restoring the guard channel as I noticed one for sale, but alas the last owner removed the mating connector as well as the various controls. The "dummy" module fitted used to be the HF version according to labelling but has been stripped completey of parts and a blank panel fitted. Maybe I should test the receiver and see how it performs. To do this I'll have to rig up a power supply and mating power connector.

First a collection of pictures

Dating evidence puts the manufacturing date as 1947.

The dial markings at first sight seem puzzling but each of the four wavebands is stretched over a huge length of dial with markings on a gentle spiral indicated by the four pointers. The dark wavy line deals with slight tuning discrepancies.

There are twin tuning knobs (fast and slow) and twiddling these moves the four pointers. The rightmost vertical knob selects the desired waveband.

After a trial rubbing with Brasso a lot of the tarnishing disappeared.

Nearly the whole receiver is finished in plating.

Maybe the first task could be to remove the front panel and clean it up and make it look presentable?

From the evidence it's possible this example was retrieved from a house clearance garage and had been modified perhaps as early as the 1960s before being stood down for something newer.. maybe after it failed. As I recall, lots of radios in my collection turned out to have nasty faults and were relegated to a loft by owners rather than disposing of them. Nowadays, let's say in the last 20 years, old WW2 vintage radios are restored but, back in the days of a flourishing government service market, new owners would extensively modify stuff. Once Japanese black boxes appeared the situation changed for many amateurs and early equipment was set on one side. Anyway returning to the R1475, also known, incidentally as a Type 88 Receiver.

The receiver's coverage is in four bands...

2MHz to 3.62MHz (60 inches of dial)

3.58MHz to 6.44MHz (60 inches of dial)

6.38MHz to 11.38MHz (120 inches of dial)

11.24MHz to 20.14MHz (120 inches of dial)

Tuning is carried out via lots of anti-backlash gears

and wavechange via a complicated series of levers.

Valve line-up as follows:-

V1 RF Amplifier CV1053 (EF39); V2 RF Oscillator CV1932 (L63);

V3 Mixer CV1347 (ECH35);

V4 Guard Channel CV1347 (ECH35); V5 1st IF Amplifier CV1053 (EF39);

V6 Voltage Stabilizer CV216 (VR150/30);

V7 2nd IF Amplifier CV1053 (EF39); V8 AVC CV587 (DH63);

V9 Detector + BFO CV587 (DH63);

V10 Noise Limiter + AVC delay CV1054 (EB34); V11 AF Amplifier CV587 (DH63);

V12 Audio Power Amplifier CV1932 (L63); V13 Tuning Indicator CV1103 (Y63).

Unlike most WW2 or immediate post-war receivers the R1475 is modular in construction. Modules are plug-in simplifying repairs (given a set of spare modules)

These are as follows:-

Aerial tuning Unit A (Type 145); RF Amplifier Unit B (Type 146); Local oscillator Unit C (Type 171);

Mixer Unit D (Type 11); First IF Unit E (Type 37); Inductance/Condenser Unit F (Type 88);

Second IF Unit G (Type 38); BFO Unit J (Type 170); Output Unit K (Type 45);

Guard Units P & Q (Type 131 and Type 132).

Power supply requirement is met by a matching mains/battery PSU (Type 360) which connects to the rear of the receiver via a 4-pin Jones plug carrying 260V HT and 12V LT. As is the case with the R1155 the HT supply supplies negative bias to the receiver and as such the negative feed is not chassis connected.

If I can find a junk box female Jones socket I can wire this to my R1155 PSU suitably modified to supply 12v LT. Alternatively I have a home-brew DST100 PSU which could be suitably modified for the job. Ideally, long-term I should make a purpose-built PSU which matches the receiver.

Removing the front panel (above) was quite easy except for the four pointers dropping off. These locate in slots in the dial and slide along the bar marked with frequency numbers. Reassembly might be tricky.. I noticed the row of module sockets had lots of loose solder joints which I'll have to deal with before reassembly.

I found I needed to drill the copper rivets holding the bar carrying the frequency numbering and detach it so cleaning it was possible and front panel paint removal was easier. Then I used a steel rule and gentle tapping with a hammer to straighten the edges of the front panel which had suffered from umpteen bumps during its life.

The last owner had used a silver crackle effect paint which was in poor condition. The paint had made the panel labelling almost disappear so the new paint needs to deal with this problem. The magic eye panel had shed nearly all its new paint from zero adherence.

It was an incredibly messy task. Removing three coats of paint (Silver hammerite, some black,and,finally original grey) using a stripper called TX10 which did what it said on the tin. Our second recent purchase from Amazon where the package was found hidden away by the back gate by a visiting lift engineer who'd spotted it. "Handed over to the occupant" it said on the on-line delivery info.

No it wasn't...

A few months back I decided to stop using these next day delivery options as it somehow seemed immoral to abandon real shops, however I spotted something I needed in Curry's recently.. I went to their store and was told it wasn't in stock but I could have it delivered within a week for an extra cost.

The panel colour above (tricky to reproduce it here true) is similar to other (cleaned) metalwork but the bezel has pinpricks of rust starting at some of the engraving. I might be able to treat this and rub it down to improve it.

The four handles (made from brass) were covered in black plastic and this was badly cracked so I removed it. Underneath was a thick coating of verdigris which I removed with a wire brush. I suppose I could use heatshrink sleeving rather than paint?

Then I cleaned up the surround to the plastic dial which was a bit rusty at the sharp edges. Rubbing down with emery cloth revealing a thick copper plating underneath.

Left is a slightly puzzling control. It connected to one of the modules but, because it uses stiff wires, one had broken away and the second looked dodgy, so I opened up the case and fitted stranded wires. It appears to be a small variable capacitor but not of standard construction and is labelled "Scale Trimmer" on the panel.

Below is the megacycle scale which I cleaned up as much as possible without damaging the lettering. As rust has taken hold under the label it will have to do. Options are to remove everything, repaint and either carefully apply lettraset or make a new lettered strip using handheld label printer.

Above is a view from the front, clearly less the front panel, with the various controls, magic eye socket and phone sockets lying loose, after I'd decided to clean up the metalwork as best I could. The steel chassis is heavily silver plated and had badly tarnished but with pock marks of rust present over most of the metalwork. The latter I had to clean off using small brass brushes in an electric drill then finish off with Brasso.

The main task is to paint the front panels and other parts, then I can reassemble everything, figure out what to use as a power supply then carry out initial testing. I'll also fit dummy controls for the absent guard receiver to make things half presentable.

Below, after painting the front panel parts.

I now have a dis-assembled abandoned project so with a fair wind I should be able to copy parts re the guard receiver whose mechanical mounting bits are missing. I had intended to use parts from the newly acquired box of bits but they're too good to scrap. This means I'll have to make new parts to replace those that are missing, for example I'm looking at the design of the contact strip to mate up with the guard receiver contacts plus a new circuit fto fit in the empty guard chassis that came with this R1475. Below... details of the guard receiver.

The guard receiver uses a crystal matched to the desired broadcast channel. This is a large-style FT241. Can I dispense with this crystal if for example I wish to receive Radio 4 on 198KHz?

I'll need to understand the R1475 local oscillator circuitry to see what's feasible.

A bad omen... I started to assemble the guard receiver chassis that came with the disassembled bits from the second R1475 and had difficulty with fitting the preset capacitors. After puzzling over this for ten minutes I realized the front panel could be fitted in four different ways but only two were possible and in both cases the newly painted surface was on the inside so I had to respray the metal plate. In fact although fitting this panel to the chassis looked easy it wasn't due to the awkward location of the fixing screws.

One tricky bit was the tuning condenser (with the black knob) which needed to be secured with spacers to push it back from the panel otherwise the end-stop bracket wasn't in line with the pointer. A clue (apart from it the end-stop not having any effect) was one spacer left over in the bag of bits for the guard receiver.

Once I'd finished reassembly I found it extremely stiff to fit in the aperture in the main front panel of my first receiver. Clearly tolerancing was an issue when these receivers were made.

I also need to make a new front panel to replace the dummy one that came with my R1475 (at least it came with those two handles). Also, I need to make a new contact strip.. read on.

The housing shown here fastens to the rear of the front panel and holds at an angle a plastic strip to which is rivetted a set of spring strips. As the guard receiver pushes into place sliding over the angled strips to make firm contact with a set of prongs.

The construction of the new contact assembly needs to be very accurate if the guard receiver mates up so the contacts accurately match the spring strips. I have the original chassis (with no electrical parts) from the assembled R1475 but I need to make a new front panel as the one fitted is blank. Maybe (if feasible) I should make the reconstructed guard receiver fit for something useful such as designing it for a broadcast station.. Radio 4 LW or a strong MW station?

I already reassembled the latest guard receiver, which at first sight is only missing its front panel (detached for repaintng by its last owner). This is necessary because I need to ensure the new contact assembly will work with the other incomplete guard receiver.

Here's a few pictures showing the construction of the spring terminal strip. I marked out eleven holes on a scrap piece of bakelite then drilled (using a pillar drill to keep the holes vertical) and tapped these for 6BA. Fortunately I had a collection of phosphor bronze strips and used some of these for the springs. As they took up nearly all the lateral space I heatshrinked the centre portions and cut a chamfer on some of the edges to keep them from getting too close. The solder ends I bent clear. The two longer strips on the right are configured as a normally made switch and I'll solder a piece of metal from a scrap relay later.

in progress