Wireless Set No. 52 Canadian - Project

[David Dunlop]

An interesting day working on the Main Set Receiver yesterday. Some mysteries solved. Some new ones added to the pot.

The first thing that came to light, literally, was the discovery of a cracked outer terminal wafer on the Wave Change (Band) Switch, S6A, located on the upper right side of the receiver chassis. I had never seen this before, and initially thought I had been the cause as this switch sits right where ones hand instinctively goes to grasp the upper side of the chassis assembly when picking it up. The only reason I noticed it was because the work lamp on that side of my bench was on when I put the receiver down and the light created a shadow on the wafer that caught my eye. A close inspection, however, revealed the inner core of the fracture was not fresh, but had discoloured over a period of time.

In the attached photo, the crack runs through the empty 5th terminal position, between the two occupied terminals at the 5:00 position on the wafer.

Studying the wafer, I then noticed the none factory soldering point on the top right most terminal, where a new, plastic covered lead was soldered into the bottom side of the terminal, rather than onto the actual terminal itself that faces inward on the other side. This new lead runs up to the S5A Relay up behind the 8-Pin Connector on the back of the receiver. My thinking is that a repair was done at some point where the two retaining screws for the wafer were removed in order to pull the wafer forward to access the necessary terminal to effect the repair, There are several heavy gauge, solid copper wires soldered to this wafer and they likely resisted moving forward at the expense of cracking the wafer. The rotating contact plate and terminals on this outer wafer are still interacting correctly, so the old lead was likely cut away, the wafer carefully reinstalled and the new lead soldered to the bottom of its terminal.

That was the most exciting part of the days work, but I now know to take extra care when I dismantle this S6A switch from my Spare Parts Receiver down the road.

David

[David Dunlop]

The game plan with the Main Set Receiver yesterday was to first look at the LT and HT Meter Readings with the receiver running off the ZE-11 Remote Supply. The last time I had done this, the meter had not been properly set to its zero mark.

Before connecting up the ZE-11, however, I took the time to check the values of all the relevant metering resisters on the receiver. They all spec’d out in the same range of values as the ones in the Remote Receiver that works perfectly, the ones in the Spare Parts Receiver and the supply of NOS ones I have on hand, some of which I had to use to replace ones in the Remote Receiver that had gone ‘full open’. So all that looked good.

Since the ZE-11 would be operating in AC Mode, I set the meter on HT and hooked up the ZE-11. In AC Mode, the Remote Supply 12 Volt output is in AC Current and cannot be detected by the LT meter circuits.

When I turned the ZE-11 on, the HT reading went up just above 180 Volts for a fraction of a second and then dropped steadily to just a whisker above the 150 Volts mark, just as the white noise audio output arrived on the loudspeaker. Under no load, the output of the Remote Supply is about 30 volts or more above required specifications for the receiver. To test the output properly in these conditions, it is necessary to connect an appropriately sized resister across the 150 Volt output terminals of the ZE-11 as a load and take the reading from there. The meter was spot on with its information. With a fully discharged electrical system in the receiver, there is no load on the Remote Supply for a few milliseconds until capacitors etc. start charging up. As the circuits charge up, the load increases and the recorded voltage drops to its normal operating point. This told me the meter was in good working order. One big step forward.

While the Main Set Receiver was out of the Carriers No. 4, and to give the receiver a chance to warm up and stabilize, I let it run and turned my attention to the Supply Unit in the Carriers No. 4. I powered up my CPP-2 and hooked up a lead to the +12 Volt terminal in the Carriers No. 4 for the receiver. Then I realized I needed a second lead to ground on the Carriers No. 4 to complete the circuit. More on that later. I reinstalled a bolt into one of the receiver mounting holes and connected the second lead to it, and hooked up my multimeter.

When I turned the switch on at the Supply Unit, I got a perfectly steady 12.3 Volts DC reading that matched the output of the CPP-2 perfectly. I then shut the Supply Unit off and switched my leads to the +150 Volt receiver terminal in the Carriers No. 4. Since the vibrator supply portion of the Supply Unit, which feds the receiver, is a very similar design to the ZE-11 Remote Supply, I expected to get a high reading here. Something in the +180 Volt range, since there would be no load on the output for it to work with. Sure enough, when the Supply Unit was turned back on, the multimeter swung back and forth a few volts either side of the 180 Volt value. This was all good information.

I know knew the Main Set Receiver was reading correct voltages and behaved in a similar manner, to a point, as the Remote Receiver when running on the ZE-11 Remote Supply. But there were LT and HT voltage drop offs when the receiver was operating in the Carriers No. 4. I returned to the idling receiver and switched on the Calibrator. The meter was now reading about two whiskers north of the 150 Volt mark and it dipped just to the 150 Volt mark but as the Calibrator warmed up, the needle returned to its original slightly high position. Equally good news.

I went back to the Carriers No; 4, and reset the multimeter to the +12 Volt terminal for the receiver and switched the Supply Unit back on. 12.3 Volts steady. I then flipped the switch on the Supply Unit for the Sender Heaters. The 12 Volt reading dropped right to 10 Volts and sat there. I powered everything off and switched over to the +150 Volt terminal again. Turned the Supply Unit back on and got the reading bouncing around the 180 Volt mark once more. Then I turned the Sender Heaters back on and this reading suddenly dove down to the 110 to 130 Volt range and bounced around there. This leads me to suspect the Supply Unit will need a close look when its time comes.


David

[David Dunlop]

With the checks on the Supply Unit in the Carriers No. 4 out of the way, I returned to the Main Set Receiver, which was still idling away, on the workbench. Several interesting things have been going on with it.

First, upon warm up, the only audio output I have had is white noise static. I typically have the receiver set on Band 2, tuned to 5.0 KC. This is a convenient frequency because it means Bands 1 and 3 are already set at 2.5 KC and 10 KC respectively and there are nearly always good SW reference signals to be found at, or very near those frequencies one can tune the receiver to quickly. It also makes checking the Crystal Calibrator on each of the three Bands relatively quick as well.

Up until now, this receiver does not detect any signals from anywhere. Just constant static. The odd thing is that usually, on these receivers, if you touch the aerial terminal when the set is on, you introduce a bias to the incoming signal that changes the audio output somewhat. If you are wearing shoes, your body acts like a giant aerial and shifts the signal somewhat. If you are in bare feet on a concrete floor, your body becomes a ground for the signal and the output changes a bit as well. On this receiver, none of that happens at all.

My approach is to start at the very back end of the circuits, right up behind the aerial tuning at Valve V1A, the RF Amplifier and progressively work my way to the front end of the receiver. The first three stages are all ARP-3 valves and all run sequentially from right to left in the upper right corner of the chassis. These are V1A the RF Amplifier, V1B, the Conversion Oscillator and V1C, the Mixer.

First thing I wanted to do with these three valves was pull the shield caps and then touch the end caps of each valve to see if that might impart a bias to the audio output. No changes at all for all three. Next step was to pull the three valves and test them again. I have two NOS ARP-3 valves that both test in the upper 80’s on my valve tester. All three of these valves checked out in the upper 70’s, very close to one another. Good news, but it didn’t shed too much light on the issues at hand. Then for some odd reason, with the set nicely warmed up, I decided to check for Crystal Calibrator signals once more.

Nothing detected at 5.0 KC on Band 2 with the calibrator set at 1000. So I switched to Band 1 and backed the dial up from 2.5 KC to 2.0. And there was the calibrator tone, clear as a bell. I switched the calibrator to 100 and once again, there was the tone, just slightly less loud. When I switched the calibrator to 10, I had to really listen to the loudspeaker, but could make out the tone in the background. That made my evening!

A quick check on Band 1 at 2.0, 3.0 and 4.0 found the calibrator signals with similar intensities. So I switched back to Band 2 at 5.0 KC. No calibrator. I backed up to 4.0 KC and there it was again. But at 5.0, 6.0 7.0 and 8.0 nothing detected at all. One last look at Band 3 was now required. Nothing detected anywhere at all on that band. Overall good news, but I now need to do some thinking about why the Crystal Calibrator signal drops off the dial above 4.0 KC.

David

[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