Wireless Set No. 52 Canadian - Project

[David Dunlop]

My apologies for taking a while to post more information on this project. I am at the point where I have a Remote Receiver that is functioning very well, but not completely checked for electrical basics, and I have no idea when it was last aligned and calibrated.

By comparison, the Main Set Receiver cannot detect a signal to save its soul and even its own Crystal Calibration Signals drop off the tuning dial above 4.40 MC. and, when it was last aligned and calibrated is also unknown.

So to start, I took the Main Set Receiver and went through all the valves to test them and did a complete Meter Reading of all its valves internally to see what that told me, compared to the manufacturers specs in the Operators Manual. Since the same Grid Circuit is used to obtain the meter readings from each valve, I also had to identify and find the Bias Resistors used in each of these valve circuits to obtain the meter readings, to check the resistors for the ability to still be providing valid readings.

The meter readings were the easy part. Warm the receiver up for 50 minutes and then turn the meter switch through each position according to the manual and write the readings down. The valve testing went really well also; thanks to the British Valve Adapter I built last year. All tested in a tight cluster in the upper 70’s on my Tube Tester. NOS valves, brand new, test consistently in the upper 80’s by comparison.

Finding all the Bias Resistors to check was another matter. Canadian Marconi Company went the route of consolidating nearly all small components related to the valves on Terminal Boards remotely located from their respective valves to make access easier, sort of.

As you will see in the first two photos, Capacitors and resistors frequently share common terminal sets and then additional capacitors get fitted next door, so access for replacement gets limited. Components on adjoining boards can also overlap, further challenging access. Then the next BIG wrinkle surfaces.

75 plus years ago, electronic components were large and lots of space was needed in a chassis to mount them. The spread between terminals on these boards is exactly 2.0 inches. That means the total length of a new resistor, or capacitor, tip to tip on the leads and the component body included was very likely 3 inches. The component could be tied to the terminal posts, soldered in place and the leads trimmed easily. To replace one of these components today, you are lucky to find any with total length greater than 2.5 inches and sometimes only 2.25 inches. Next to no wiggle room. One has to be very careful planning to work out.

What I did discover, however, is that CMC mounted these Terminal Boards of small hollow steel tube standoffs about one quarter to three eighths inches long. The base end is essentially a hollow tube rivet that gets fastened to the chassis and the other end is threaded to take a slotted, round head machine screw and external toothed lock washer to mount the board. Removing the screws, hopefully, should allow the boards to be carefully manoeuvred a bit to gain a little more access to components needing replacement.

The last wrinkle was I could not find the R20D Bias Resistor anywhere for valve V1B. Checking Allan Isaacs work in England on these receivers, I discovered he could not find it either. I put a call out for help and Jacques Fortin eventually replied, complete with photos to show me this resistor and a related Grid Leak Resistor were actually mounted on a tiny little terminal strip directly underneath V1B at the front of the receiver. The Grid Leak Resistor can just be seen, left centre in the last photos with the Green, Black and Orange bands painted on it. The all-important R20D, Bias Resistor is hiding directly behind this one, completely inaccessible without performing a 2nd to 4th Echelon Repair.

So now I have all the initial data for the Main Set Receiver and have crafted a spreadsheet to log it all in. Next step is to repeat the process with the Remote Receiver, so I can compare notes between them.

David

[David Dunlop]

You may have noticed a lack of postings lately. Some of that is certainly due to Life getting in the way of Hobbies from time to time, but in this instance, the bulk of it is simply me, having to shift gears from a ‘Mechanical/Physical Restoration Train of Thought’ to getting my brain wrapped back around the actual electronics of the project once again. I have been away from that for a year or so now and it shows. Sketchy surviving 2nd to 4th Echelon Documentation for the 52-Set does not help much either.

With the receiver portion of the project, I do have the benefit of three on hand. The Remote Receiver is performing very well and has become my benchmark to compare the Main Set receiver to, in the course of getting it back up and running. Parts of the Main Set receiver are working well. Others barely. The net result is lots of controllable static audio output. End of story.

The third receiver is the Parts one. Useful for comparisons to the other two.

Most of my time recently has been spent designing Spreadsheets on Excel to log data into, as I collect it from the Remote and Main Set Receivers. The general plan is to log as much information as I can from the Remote Receiver and then compare the same data from the Main Set Receiver to try and narrow down significant anomalies for more detailed investigation.

So far, all valves in both sets have been tested and the Meter Readings of each receiver recorded, along with the relevant resisters in the meter circuits. The valves are all rating as new and several resisters in the meter circuits of the Main Set Receiver will need replacement.

I am now completing a pin-by-pin analysis of all the valves in the Remote receiver for both Voltage and Resistance measurements. That work has been done with the exception of V1A and half of V1B. These two sockets are hiding up behind the 8-Pin Connector assembly, which will have to be unscrewed from the chassis and swung away to complete the tests.

Then I can repeat the process with the Main Set Receiver and narrow down significant variations for a closer look.

While doing this work, I was chatting with Jacques Fortin and he asked if any of the receivers had Modification Instruction 6 Performed on them. I had forgotten about this one. It was issued 24 April 1959, and involved replacement of the 10 original 100 uuF Trimmer Capacitors in the IF, BFO and Detector stages of the Receiver.

The originals, a semi-fixed 5-100 uuF capacitor were found to be defective and were to be replaced with a newer improved variable, air dielectric 7.5 to 99.9 uuF capacitor.

The distinguishing characteristics between these two sets of variable capacitors visually, is the originals had a flat zinc plated finish on the tuning shafts and locking nuts and the shafts stuck out beyond the locking nuts about one quarter inch. The new replacement trimmers have a bright nickel finish and the shafts sit flush with the locking nuts.

The Modification Cards in my Remote Receiver and Parts Receiver confirmed the change was done in 1961 on the remote Receiver and never done on the Parts one. The first two photos attached show the originals in the Parts Receiver and the second set of photos show the upgraded capacitors in the Remote Receiver. C7A to C7H can be found in two banks of four at the back of the chassis. C7K and C7J are found, left to right, at the front of the chassis on the extreme left directly above the retaining clamp for valves V1G and V1H. No letter “I” was used in the coding system for these trimmers.

I thought I would post this information in case anyone has a 52-Set Receiver with no Mod Card. They can at least now determine if their receiver was modified or not.

David

[Mike K]

Hi David

I am not a radio tech by any stretch but the normal method of testing tube receivers was to check each stage at a time . They used to use a VTOM , VTVM or oscilloscope and compare the readings of each stage to the figures found in the service manual. Maybe you could measure the stages of your receivers and compare them and get an idea of where the problems are.

[David Dunlop]

Good Evening, Mike.

I too am about as far away as one could ever get from being a qualified radio tech. My entire training was a one Year Electrical Shop Class in Middle School back when Spark Gap Transmitters were still a popular means of delivering the Evening News!

You are quite right, however, that a logical troubleshooting search can be accomplished following the basic Block Diagram flow of the major circuits from the R.F. Amplifier at the Aerial end to the A.F. Amplifiers at the Loudspeaker/Headphones end. The valve and component layout within the receiver chassis follows this flow visually, in a very good manner. It is the 2nd to 4th Echelon Maintenance Manual that I find very unnerving.

I have the Wireless Set No. 19 Mk III 2nd to 4th Echelon Manual as a comparison. It is a brilliant work. It starts with a brief introduction to the set; a massive Table of Contents (the manual is some 400 plus pages) and a list of test equipment required and support items to be fabricated. Then off it goes with a very logical step-by-step analysis, with relevant disassembly instructions when and where they are needed. It is a very good manual for step-by-step work and how to do it.

By comparison for the 2nd to 4th Echelon Manual for the 52-Set, there is no list of test equipment needed and no table of contents/index at all. The first five steps in the manual are:

- Meter Calibration.
- Switch Connections (pages of exploded diagrams of switch connections).
- Cleaning the Crystal
- Dismantling the Flick Mechanism,

And then suddenly you are in:

Alignment and Specification Testing:

I.F. Alignment.

If you plod well into the manual, about two thirds, you eventually discover 12 Point to Point Voltage and Resistance Charts for the Main Set Components, providing the factory original electrical specifications for each point to point test.

I am currently replicating three of these charts for the two receivers I have available. There are a couple of more for point to point tests from the various valve pins to either switch contacts, or terminals on the 8-Pin Connectors. I hope to replicate them as well.

Time consuming, yes. But what else is there to do with Covid running amuck? Sigh! It should mean I have become very familiar with the innards of the receiver when I am done and given the electronics sections of my brain a good dusting off in the process. My hope is I end up with a set of factory standards and a set of specs from a fully working 75-year-old receiver to compare those to. That would give me an acceptable range of specs the receiver is happy to work within. Then I can see how the specs from the non-working receiver compare, so that I can narrow down exactly what has to be replaced. The more parts I can order in one shipment from a supplier these days, the better.

As long as I don’t grow cataracts in the meantime, I am laughing.

Stay safe Mike!

David

[David Dunlop]

I have been looking at my Remote Receiver now since January of 2018, but only just saw the upper mounting hardware on it this last weekend.

When it arrived in the mail, the two upper ¼-inch hex bolt assemblies were installed from the outside of the case inward, so the lock washers and hex nuts were on the panel side of the case. This had always looked OK to me as the heads of the bolts were on the outside and did not protrude any significant amount. I looked streamlined. It looked nice.

Whenever I needed to work on the Remote Receiver, I removed the four sets of mounting hardware and pulled the receiver out of its case, worked on it and put it back. For the very first time in over three years last weekend, I had to check something quickly on the Crystal Calibrator, so decided to simply remove the upper front panel of the receiver to have a look. I could not do that. The two ends of the upper panel, once it was unlatched, kept hanging up on the upper mounting hardware, and no matter what sort of angle I attempted with the upper panel, it would not come free. So I locked it back in place and had a closer look. And eventually, I saw for the first time what I was looking at.

The cut-outs on either end of the upper front panel of the receiver are designed to clear the thinner heads of the ¼-inch hex bolts, NOT the thicker and longer shank ends. Note the attached photos. That is also why the upper hardware holding the main set receiver in place in the Carriers No. 4 also has its hardware feeding towards the Supply Unit on each side.

It took three years, but I finally understood the design.

David

[David Dunlop]

Not a very productive week at all in so far as the 52-Set Project goes. I did get another spreadsheet drawn up for logging the Voltage Values deemed relevant from all the receiver valve by Canadian Marconi Company in the 2nd to 4th Echelon Maintenance Manual, and have now got those values from the Main Set Receiver logged in. Still a lot more of this sort of analysis to finish, however. I did find one interesting thing through all this though.

Another oddity has surfaced related to Valve V2B.

All the valves in the 52-Set Receiver utilized directly heated filaments and this is typically provided directly from the battery voltage used to power the set. In this case, 12 Volts DC. With North American valve production, these filaments, or heaters, are connected to Pins 1 and 2 on the base of the valve. The valve pin numbering system is different in the UK, so going at least as far back as the Wireless Set No. 9 Mk I*, CMC converted the valve pin numbering system used on the British Based Valves to North American standards, to avoid any confusion on the assembly lines. So for all the valves in the 52-Set, then, Pin 1 will be the Plus side of the 12 Volt Heater circuit and Pin 2 would be the return side.

So one of the voltage checks for the 52-Set Receiver is to see that the filament/ heater circuit is working and to do this, you take a reading from Pin 1 to Ground on all of the valve sockets to confirm 12 Volts is present. If you get nothing on your meter, the Pin ! circuit is open and the valve has failed, or the heater circuit ahead of the valve socket you are testing is broken somewhere.

During this test process on the Main Set Receiver, I arrive at Valve V2B and got a reading of ‘0.004’ on my meter. Odd, because I had just tested all the valves a few days ago and this one was working perfectly. Even odder, because I am looking at the valve and can clearly see the heater glowing happily away at the top of it. We can even kick it up another notch! This has been the reading I have been getting from Pin 2 on all the other valves up to this point. So I check Pin 2. I get a meter reading of 12.71 Volts, which is exactly what I have been getting from Pin 1 on all the other valves, and which is a match to the output voltage from my ZE-11 Remote Supply Unit.

When I look at the wiring on the bottom of the V2B valve socket, it is all undisturbed, factory original soldering. Mystery solved. Somebody made a mistake on the assembly line wiring up this particular socket. In fairness, the mistake is no big deal as the Heater Circuit is isolated from all the others in the receiver and the heater will work happily wired either way. What got really interesting, however, was that when I got around to the same testing on the Remote Receiver several days later, the same result was found. At that point, I also decided to check the spare receiver. Same thing. All factory original soldering and all soldered with Pins 1 and 2 flipped.

There is no logical reason for wiring these two pins in this way deliberately, so my suspicion is that this was likely an error in the production line assembly instructions drawn up for the work station involved with wiring in the heater circuit connections for the V2B socket. The error was missed and never found and corrected.

Interesting what one can discover 75 + years after the fact.

David

[David Dunlop]

Not that much of interest going on with the 52-Set lately. I have pretty much finished all the test measurements for the Remote and Main Set Receivers and can finally sit down and compare the two between each other and the specifications in the manuals.

Out of curiosity, I did do some random tests on several capacitors and resistors in the Spare Parts receiver and was pleased to discover they were all still within original specifications. With that in mind, I have decided the next step in this project will be to strip the Spare Parts receiver of all retrievable components, starting with the four Tag Boards holding the majority of the resisters and capacitors and work my way through it until just the chassis frame is left. A couple of extra plastic storage bins should be enough to get all the parts, including the two front panel sections put safely away.

This will serve a number of purposes. I can reuse original parts were appropriate before having to source modern replacement look alikes, which are getting more and more expensive with minimum order amounts and trans border shipping, and also free up a huge chunk of shelf storage space where the three wooden accessory boxes for the 52-Set will eventually reside.

David