R1155 progress

Restoration of the R1155L is not progressing well at the moment, digging into some of the more inaccessible areas has uncovered a number of burnt resistors and wiring around the bias board. Most of the burnt bits appear to be part of a modification done by a previous owner, who in future I'm going to refer to as Bill the Bodger (a British term for a person who makes or repairs something badly or clumsily). His shoddy efforts have really created a lot of additional work for me.

It looks like Bill has attempted to re-wire the Meter Amplitude potentiometer into the bias circuit, although without a lot of effort I'm not going to find out why. I'm guessing that it might have been intended for variable RF Gain, but whatever it is it will have to come out.

On a more encouraging note, I was delighted to find that the two VI103 'magic eye' indicators I bought last month are both usable. The R1155 uses one as a tuning indicator, driven by the AGC voltage. Unfortunately the phosphor that gives the green glow seems to fail very quickly, resulting in a very dim display even though the valve emission is still good. Finding serviceable originals is now very difficult; New Old Stock (NOS) near-equivalents are available, but these are getting expensive.

VI103 'Magic Eye' on test, control grid grounded.

The seller said they tested OK on his AVO valve tester, but he didn't give any indication of how bright they were. They probably aren't as bright as they should be, but they are usable and at the price I paid I'm definitely well pleased with them. The seller was in Eastern Europe, so it might have been interesting to find out how two British Air Ministry valves got there.

From Eastern Europe via eBay!

The original VI103 in my set had been replaced with an EM34, a similar civilian indicator with a slightly different 'eye' shape. Fortunately I have now discovered that the pin out of the two types are slightly different, so the wiring of the socket must be changed back before I re-install a VI103!

Stuffing!

Old wax paper capacitors are notorious for going leaky. Even if they are not significantly leaky now, you can guarantee that they will be at some time in the future. My approach is usually to change all such capacitors on sight, and this receiver will be no exception to this rule.

Unusually, in the R1155, the decoupling capacitors are all housed in aluminium cans bolted to the chassis. Most of these have three 100nF capacitors inside, others have only one. I want to preserve the original appearance of the chassis, so I will be removing the contents of these cans and replacing them with modern components.

One of several capacitor cans

Removing a can from the chassis is easy. You just cut the existing wires close to where they enter the can, leaving the wires connected so you can see where you have to connect the new wires. Undoing the nut and pulling the can from the chassis completes the easy part of the task!

At this point you have a choice in the method for opening the can. Some people use a pipe cutter to separate the cylindrical part into two pieces, and then glue it back together afterwards using epoxy. Foil tape can be used to hide the join. Others may use a hacksaw to remove the end of the can, and glue that back in place afterwards. 

Fortunately I discovered an easier and neater way to do it.

Once the capacitor can has been removed, put the nut loosely back onto the threaded part. Clamp the nut in the jaws of a small bench vice with the capacitor standing vertically upwards. Now grab the end of the can and carefully rock it back and forwards, and side to side.  The cylindrical part of the can is crimped on to the threaded base part, and this rocking motion will loosen the crimping.  The trick is not to be too rough and tear the metal! Carry on this gentle loosening process until you can pull the can vertically upwards and separate it from the threaded part, which stays in the vice.

Removing the original capacitors from the can. Messy!

Carefully dig out the black pitch from the open end of the can with a small screwdriver. The now exposed capacitors inside need a bit of persuasion to come out of the can.  I use a large wood screw to do this; just screw it into the waxy yellow mass inside the can and pull it out.

In the next blog entry I'll tell you how I re-stuffed this can with new capacitors and re-assembled it.

Keep listening!

A little distraction

I've not made any progress with the R1155L since it appeared on my workbench earlier this month. It's still there, it just got pushed to one side. I've not been idle though, over the last couple of weeks I've been building the power supply and audio amplifier that I will eventually be needed to run the receiver. I could have built one with modern components, but I decided that a valve (tube) design would be more appropriate.

Front view. The hole is for a neon 'HT on' indicator.

The power supply is built onto a simple folded aluminium chassis purchased from a seller on eBay, and in the best tradition of radio recycling, most of the parts are recovered from other radios and electronic equipment. After the chassis the most expensive item was the 5Z4G rectifier valve, although the KT63 tetrode could have been quite costly if I didn't have one already.

Rear view of KT63 (left) and 5Z4G (right)

The transformer was the most difficult item to source. With multiple windings to provide HT, rectifier heater and LT supplies, this style of transformer probably hasn't been manufactured since the 1960s when silicon diodes began to replace valve rectifiers. An R1155 (especially one with the DF valves refitted) will require more heater current than most domestic radio transformers could provide, so I had to limit my search to old industrial and military equipment. Fortunately last year's visit to the National Vintage Communications Fair in Warwick proved to be very worthwhile, and I came home with both a suitable transformer and a choke to go with it.

Underside view. All wire is silicone insulated, except for AC cable.

The connection to the power supply are brought out to a tagstrip on the rear of the chassis. HT- and chassis are on separate terminals, and the LT supply is also isolated from the chassis. This will allow me to add wire links as required for use with either my R1155 (floating HT & grounded LT) or my HRO receiver (grounded HT & floating LT).

The PSU is now working, but for safety's sake it needs to be finished with some form of case. There are dangerous voltages on the transformer terminals just behind the rectifier valve, and also below the chassis.

Building it has been an enjoyable distraction, and its actually the first bit of valve equipment that I have ever built from scratch. Now I need to face the more difficult task...the R1155 itself.

Keep listening!

R1155L first observations

I've had my R1155L receiver for around 3 months now, but today was my first opportunity to get it on the bench for a proper inspection.

I always knew that restoring an R1155 would be a challenge. Even though I knew just how tightly everything is packed into the chassis, with very poor access, actually seeing it close up was a bit of a worry! The R1155 was never designed with maintenance in mind; but with the average wartime life of a Bomber Command aircraft measured in weeks, why would it have been?

As was immediately apparent when I purchased the set, some fool has cut off the pins of the Jones plugs and soldered to the stumps left behind. For God's sake, why would anybody do such a horrendous bodge? If a suitable socket could not be found, then surely soldering to the intact pins would have been sufficient?  I now have the difficult task of replacing these plugs, and it looks like getting access to the screws that hold them in place is going to be a really big problem.

The bloke who bodged the connectors?

I had also noted that VR102 (V9) and both of the VR99As (V1 & V2) are missing. These are part of the DF circuit, and were often removed by Hams to reduce the heater current required by the set. As part of a loudspeaker amplifier modification, V1 had been replaced with a KT63 Beam Tetrode. I had already removed an output transformer which had been added above the chassis, as well as a dreadful 'birds nest' of  capacitors and resistors that had been added under the chassis. These have now been removed, along with any wiring that obviously wasn't original.

DF Section (V1 & V2). Yellow arrows indicate cut wires.

An initial poke around revealed a few more things. It also gave me the opportunity to take some 'before' photographs, which I often forget to do.

The VI103 'Magic Eye' tuning indicator has been replaced by a later civilian type EM34. This isn't totally unexpected. The phosphor on these devices has a short life, and they are often found to be glowing only very dimly, even though the cathode emission is still good.  Unfortunately as the EM34 is a smaller valve, the metal tube it mounts in has had to be made shorter.

Modified Magic Eye

The wiring to both the Meter Amplitude and Meter Balance potentiometers has been modified. The reason for this is not immediately obvious, so I'll have to compare the wiring with the circuit diagram and work it out.

Meter Amplitude & Meter Balance pots. Arrows indicate cut wires

There is a bit of blackening under the chassis below the volume control. It could be soot from a burned up resistor, although the culprit couldn't be seen. Another resistor has been added here. I know access is difficult, but it could have been done a bit more neatly.

Something has been getting hot. Note added resistors; quality job what!

As well as the valves, the set is also missing two tubular aluminum cased capacitors from the DF stage. The bases for V1 & V4 are also missing the aluminium collar onto which the screening can fits. I have spare screening cans, but not the valve base collars, so these have been added to the shopping list.

Holes for the missing capacitors, and a valve socket without the screening collar.

This valve socket should have a collar like the one in the photo above.

On the good side, my initial observation that the set was free of perishable rubber insulated wiring has proved to be 100% correct, so there should not be any need for a re-wire. In fact it appears to be PVC, so I need to be careful not to melt it accidentally with the soldering iron.

Restoring this one is going to be a long job. I also have to  make a power supply for it. More blogs will follow as (hopefully) I make some progress.

Keep listening!