19 Set restoration - Part 2: Initial Radio checks

As I mentioned previously, my 19 Set is a British MKIII one that had that had been rebuilt by REME sometime after WW2, probably in the 1950s.

These rebuilt examples are not to the original spec, having been rebuilt without the VHF 'B' set, but they do have the advantage of having been re-wired with pvc insulated wire. Original WW2 sets may have multiple faults due to crumbing rubber insulation.

My 19 Set as received..note grey colour paint

Everything on the front panel was present and correct, apart from a missing handle on the right hand side. Once the case was off, a quick inspection showed that chassis was complete and as it should be, apart from a high wattage wirewound resistor above the chassis that was obviously not original; I'll come back to this later.

On top of the chassis, adjacent to the PA valve there is a small paxolin board bolted to the chassis with a number of capacitors and resistors on. At this point I hadn't studied the manuals and the purpose of this board was not clear to me, but I did notice that one of the wires (actually the centre conductor of a bit of coax) had broken off one of the tags. It was obvious where it should go, so I soldered it back on. The mica capacitor in the photo looks like it is broken, but is actually OK.

'Broken' capacitor and detatched wire.

The 19 Set has a large number of decoupling capacitors, mostly 100nF. These appeared to be military quality (metalised foil possibly)  types.  With the older type wax paper capacitors my usual approach is to replace all on sight, but the number of capacitors in the 19 Set would have made this a very big job. Instead I just removed three of four for testing on my AVO component bridge. All were very close to their intended value with no leakage indicated, so I just popped them back in. There is a slight risk in doing this, and I may yet have to replace some if they prove to be leaky later on

I did however replace the one on the audio amplifier grid (usually referred to by restorers as 'that capacitor') and those decoupling the AGC line as these are areas where even a small amount of leakage could seriously upset things.  I also replaced all of the small number of electrolytic capacitors, which fortunately were easy to get at... which most things in a 19 set are not!

Checking resistors is easy and in most cases can be done in circuit. Some of the higher value ones had gone up in value, but most were still in tolerance. I did end up changing a few, like the 470K visible in the photo below. The green screw head is the adjusting slug of the BFO coil, which I'll come back to later.

Replaced capacitor and resistor

So far, so good; everything looked ready for a power up test.

19 Set restoration - Part 1: Power Supply

Having won my British WS19 MKIII on an internet auction site I was able to collect it person and check that it was as good as advertised before handing over my cash. Had this not been possible then I might have been reluctant to bid as high as I did.

However it came without its companion power supply, so having confirmed that the radio was indeed a suitable candidate for restoration, my next task was to find a suitable power supply to go with it.

The power supply that I eventually acquired is the PSU No.2 MKIII, Canadian version, which uses a uses a single dual-output dynamotor to produce +275V HT for receive and +500V for transmit. This differs from the British version which has two separate dynamotors, although both types are are interchangeable.

The Canadian version also has a receive-only 'vibrator' mode which uses a mechanical vibrator and transformer, and this usefully reduces the current drawn from the battery. It is also much quieter, although it is doubtful if this would have mattered much in a tank! In vibrator mode a relay starts up the dynamotor whenever the PTT is operated.

The power unit that I received had been quite badly hacked about and 'modified'. A length of 3-core cable emerged from a hole drilled in the front panel, with the remains of a UK-type mains socket on its end. Apparently this was a common post-war modification and some modified units were re-sold for use as inverters for caravans!

Top view showing relay and large capacitor

Most of the changes were easy to undo, apart for the relay from which several contacts had been removed. As can be seen from the photo, this relay is rather specialised and is possibly unique to the 19 Set, but surprisingly after only a few weeks searching I came across a New Old Stock (NOS) item from an internet seller. It wasn't cheap, but I decided that having a fully working supply was worth the outlay.

A rather special relay

After fitting the new relay, the next job was to replace the electrolytic capacitors. There are two 20uF 450V caps in a chassis mounted can adjacent to the rectifier valve.  I couldn't manage to remove this from the chassis, so I fitted replaceements under the chassis, hidden as best as I could. The large capacitor on top of the chassis was extracted from its cardboard tube. The end disc with the terminals was removed and the remains of the capacitor discarded. The leads of two new capacitors were passed through small holes made in the disc and soldered to the terminals. After adding some packing material to the tube (to prevent it it being crushed when the fixing clamp was tightened) the disc and capacitor assembly was glued back in place.

Re-stuffing the big 32uF capacitor

I replaced all but one of the paper capacitors, using mostly 100nF 600V polyester types. This was quite time consuming, as access to some of them was very difficult (and to one impossible!) Having struggled for a while I did manage to remove the front panel for better access, but all my attempts to further dismantle the unit failed. For this reason I was also unable to re-grease the dyno bearings, so instead I setted for running a few drops of oil into each one.

Side view - not much to see!

The cold cathode OZ4A rectifier valve was missing. I could have fitted slicon diodes in it place, but I was able to find a NOS replacement from an internet auction site quite cheaply.

The mechanical vibrator was also missing, so instead I installed one of the excellent solid state replacements available from http://www.royalsignals.org.uk/vibs/. I bought a ready built plug-in replacement for the original vibrator, but they do have part assembled options if you want to hide one in an original casing.

Finally the fuses were checked and replaced with the correct values.

The unit isn't completely silent in 'vibrator' mode as you can still hear a buzz from the transformer laminations, but the improvement in reliability and efficiency is well worth the cost of the solid state upgrade.

The job had taken quite a bit more time and money to restore than I had expected, but I think the result was worth it.

The next task was to obtain the so-called 'dog bone' cable that connects the power supply to the radio.

Wireless Set No.19

Keeping the blog updated during the summer months has always been difficult for me, and this year has been even more busy than usual.  I thought I'd take advantage of a bit of spare time over Christmas to bring the blog up to date

Just before Easter I started  work on my Wireless Set 19, which turned out to be my biggest project in several years.

WS19 in Sherman tank 1943 (National Army Museum Copyright)

The Wireless Set No 19 was designed originally for tanks and armoured fighting vehicles used by British and Canadian forces in WW2, but later also used extensively in jeeps, trucks and even as a man-portable ground station. There are many excellent sources of  information on the internet so I won't go into great detail here, but the WS19 provided two radios in one box, plus intercom facilities for the tank crew.  The 'A' set was for HF W/T or R/T over longer distances while the 'B' set was used for very short range VHF comms between tanks.

My first experience of the iconic '19 Set' was as a kid in the 1970s. Thousands of sets had been sold as army surplus in the 1960s and although I never owned one myself back then, many radio amateurs that I knew did. 19 sets were often heavily 'modified'  or even broken up for spares without too much thought, as they were cheap and pentiful. 40-odd years later 19 sets and accessories have now become very collectable and sell for big money on internet auction sites. I recently saw a complete (but not guaranteed working) WS19 station with an asking price of nearly £1000!

Sometime after the war, large numbers of 19 sets were completely rebuilt (without the 'B' set) and many were then put into storage. Markings on the front panel of my British WS19 MKIII suggest that it was rebuilt at the Newark workshops of the Royal Electrical & Mechanical Engineers (REME). Unfortunately the date has been rubbed off, but based on similar sets I've seen I expect that it would have been late 1950s.

My WS19 MKIII

In the next blog I'll describe what I had to do to get the set working again.

Keep listening!

A troublesome trio

If you read my previous entry you may remember that I was debating whether to put my R1155 or my WS19 at the front of the restoration queue. I had almost decided to concentrate on the WS19, as it appeared require less work to return to working condition, but then three unexpected and more urgent jobs arrived... all of them HF transceivers!

Clansman RT320,  PSU module removed

 My Clansman RT-320 developed a (nasty) power supply fault

Yaesu FT-757GX

                              My Yaesu FT-757GX had frequency stability problems

Alinco DX-70TH

And finally my Alinco DX-70TH failed
with a duff PA driver transistor!





I was able to start investigating the WS19 power supply while waiting for the Alinco's transistors to arrive. By late in February with all three troublesome radios working again, I was finally able to clear the bench and turn my attention back to restoration work.

More details will follow soon.

Keep listening!

Happy New Year 2018

I can hardly believe that my last blog post was in February 2017, almost a year and two months ago!

I've been meaning to post more radio repair and restoration activities on here, but as often happens, life gets in the way.  It became obvious quite early in 2017 that I wasn't going to get many projects done before the summer's busy period, and this was pretty much how the year continued right up to Christmas.

This time last year I was looking forward to getting my WW2 R1155 receiver sorted. At first all seemed to be going well, with just a bit of re-wiring needed, a few capacitor replacements and some new connectors, all of which I had managed to source.

Unfortunately as I began to dig deeper into it I found some burnt components and wiring that had gone unnoticed in my initial investigation, a discovery that effectively turned a relatively straightforward task into a very much bigger one. By early March an increasing shortage of spare time forced me to abandon the job and put the set back on the shelf for another year.

It wasn't all doom and gloom though. In September, some friends and I were invited to run an Amateur Radio station at a 1940s event held at an Airfield Museum. We didn't really know what to expect from the event and had very little time to prepare, but we did manage to make a few contacts  across Europe on 40 Metres using my 1943 HRO-MX as the receiver. We've been invited back again for 2018, this time with a better location and plenty of time to put together a better range of equipment.

'Y'Service re-enactment with HRO-MX

In the autumn I managed to get my hands on a Wireless Set No. 19, an HF transmitter/receiver that was used extensively in British Armoured vehicles and Jeeps during WW2.  I've wanted one of these for years but they are getting quite scarce now, and even very poor condition sets change hands for silly money. It does look like I've been lucky to get a good one for a sensible price, but I'll save the details for a future blog entry.

I've yet to make up my mind whether to do the R1155 or the WS19 first. Either way, January in the Radio Recycling workshop is going to be interesting.

Keep listening!

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!