Wireless Set No. 52 Canadian - Project

[David Dunlop]

Finally, my first look inside this section of the Sender chassis. What struck me was how clean everything was, with little or no dirt and most important, no sign if heat discolouration or burnt smells lingering about.

The most notable thing was the pristine looking L31A COILS, RF sitting front and centre, complete with its CMC Part Number stamped on the side of it – CMC 119-209. I am not sure what prompted me to do it, but I decided to run that number against the Parts List at the back of the Operators Manual. Did that ever turn up the excitement!

According to said Parts List, L31A had Part Number CMC 119-107. The number stamped on the assembly in my Sender was nowhere to be found. So next stop was the 1945 Illustrated Parts List. It showed L31A as being, COILS, RF, 1.75-4-mc, MO, No. C1. It had a 1-1/32 inch diameter with two riveted 6-32 mounting screws at one end and no sign of a central, adjustable core. The ZA-Number reference given was ZA/CAN 4355.

A pail of tea later, I decided to check the 1948 Issue of the Illustrated Parts List for a possible explanation. Bingo! The same reference for ZA/CAN 4355 was found, but this time, directly below it was a second item, ZA/CAN 4221. It was a stink smaller diameter and was fitted to its mounting Bracket, that also held the central, adjustable iron dust core. So this complete assembly bears the CMC 119-209 Part Number.

My thought is the original design, in theory, allowed for replacement of either the coil, or the core, but the amount of work required to do either, was more than making the Coil and Bracket a single item replacement. Interestingly, the Bracket itself does not show up at all in either the 1945 or 1948 Illustrated Parts Lists. Having confirmed at this point that all the components in the Master Oscillator Tuning Circuit were replaced during the Senders last overhaul when in service, I then traced the connections to Pin 1 on the V5A Holder (socket) and found nothing worth a red flag. To be on the safe side, I retested the resistance of this Pin circuit to ground after getting a good clean contact point on the pin and now found the reading to be a steady 1.25 meg. I liked that reading and took the time to recheck Pin 1 on V5B and V5C in the same way. They both now showed 1.25 meg as well. So I was glad in the end to have opened up the shielding plate for this circuit and had a closer look.

The surprises were not quite over, however.

David

[David Dunlop]

While rechecking the Pin 1 terminal on the underside of the V5A Socket, I had noticed the two rivets securing the retaining ring on the socket to the Sender chassis floor. There was something odd about that, so I decided to look up what the Illustrated Parts List had to say. It would be an easy item to find because the Holders (sockets) for the 813 and this particular 6V6G are the only Holders in the entire 52-Set that are made of porcelain (Steatite).

As expected, it was easily found but the one in my Sender was now clearly confirmed to be a replacement item as well during the 1966 Overhaul. The attached illustration from the 1948 Issue of the Parts List shows this Holder as being of the Ring Retained style, not the riveted retaining plate as per mine. So perhaps the originals were discontinued for some reason, or got too expensive by 1966.

The last photo in this Post is of the Plate after all the dirt and dust bunnies were cleaned off the inside face.

To reinstall this Plate, at least on a Canadian Sender with the Modification Card Holder fitted, the best way is to let gravity help you.

Turn the Sender onto its left side so the heavy side rail of the chassis is on your bench. Slip the end of the Plate with the two tabs carefully down behind the rail and tip the other end in towards the bottom of the chassis. Then press down gently on the long tab at this end until it slips past the partition it fastens to and push it home until you can see the screw holes in the partition holes. Use a small nail, or similar item to centre the two screw holes and install the two screws half way home. Flip the Sender to its right side to put the two chassis rail holed to the top, do the same centering trick and install these two screws carefully home. Make certain, however, that the left hand screw in Photo 1 of Post #854, just clears the chassis rail lip it near. if not, it will hang up on the lip and dig into your bench top when you least expect it. don't ask how I know. You can then tighten the other two all the way.

If you are lucky enough to have a UK Service 52-Set Sender, you will have much better control of the Plate with a finger in the hole intended for this purpose.

Next step will be a close look at what is going on with V7A, the 813, where some seriously high resistance results were showing up.

David

[David Dunlop]

I have been looking at the test results for Valve V7A (the 813) this morning. It is quite a comprehensive set of tests in its own right for this valve. Everything gets checked twice, in each of the Power Settings, LOW, MEDIUM and HIGH and the Mode of Operation Switch set to RT. Then you repeat the tests with the Mode of Operation Switch at any of its other settings, M.C.W., CW or BREAK IN.

What I finally noticed was that the vast majority of the extremely excessive readings I got took place in the RT Mode. By excessive, I mean results that should have been 10,000 Ohms, or between 1 and 2 Megs, were coming back 25, 200, 500 Megs or Infinity.

Something definitely is not right. The test indications of an excess load lurking somewhere match up with the observation of the Supply Unit being hit with a massive load with both Dynamotors running in SEND Mode in order to check proper operation of the Receiver Isolation Relay. That prompted a quick shut down of the set as soon as proper function of the relay was heard. A careful visual examination of the Sender shows no heat discolouration anywhere. Nor are there any burnt smells anywhere, and the Supply Unit continues to function nicely with the Sender out of the Carriers No. 4 circuit and on the bench alone.

I do wonder if the Mode of Operation Switch may have a buildup of oxidation on its terminal wafer connections that I missed, so to rule that out, I am going to give that switch a couple of cleanings with Dioxit today and then repeat the set of tests for V7A. Nothing may change, but at least I can rule the possibility out and know the Mode of Operation Switch will now be nice and clean.


David

[David Dunlop]

I was able to give the Mode of Operation switch a couple of good cleanings with Deoxit the other day, which produced some positive results regarding the resistance tests for the V7A (813) Socket Pins.

First, the suspect results on Pin 3 all dropped by nearly 250,000 Ohms and are all now in a quite acceptable range. There was also an improvement in a couple of the readings for Pin 4. One reading should be 40,000 Ohms and I was getting ‘Infinity’ initially. I now get 60,000 Ohms. The second reading is supposed to be 11,000 Ohms and it was also initially giving me ‘Infinity’. It now reads 700,000 Ohms. Neither is acceptable yet, but at least I have hard numbers to work with. Every little improvement helps.

In the course of doing all this work, I stumbled across a mystery on the Circuit Diagram for the Sender, as published by Canadian Marconi on Page 203 of the Operators Manual. Still have not got it all sorted out yet (maybe never will) but I will document it all shortly.

By the way, with regards to Circuit Diagrams for the 52-Set, should you ever need them, trust only those published by Canadian Marconi Company in the Operators Manual for the 52-Set. There is another set out there redrawn and included in an evaluation document for the 52-Set. These ‘copies’ have a lot of missing information and mistakes in them. Not at all reliable for serious repairs or servicing.


David

[David Dunlop]

Having now got the suspect circuits narrowed down from the first Sender Resistance Test, the next step was to trace those circuits out on the Sender Circuit Diagram in the Operators Manual and list out the components found on them. Each component can then be checked out individually to see if any faults show up.

While doing this over the weekend for the Pin 4 circuit of V7A (813), I ran across a couple of small symbols I had never noticed before on the Sender Circuit Diagram. They were basically small little circles with a ‘Dot’ in the middle. The circuit line ran up to the circle and stopped, and 180 degrees opposite, continued on its way. A small number was written to the upper right of each of these circles and I eventually found nine of them. All were located in the front section of the Sender, between the Master Oscillator Tuning and the Power Amplifier. Oddly, there were no Comments, or Notes, to be found anywhere on the Sender Circuit Diagram to explain what these symbols were. No references at all. In fact, the Sender was the only one of the four main components of the 52-Set to have these symbols.

In the past, I have run across similar types of markings on equipment circuit diagrams, but they have always been referenced and turn out to be test points to take Meter or Scope readings at, and the circuit documentation includes values, or images of the results to expect under various circumstances. I bounced the discovery off the 19-Set Group in the UK and they were just as puzzled and came up with similar test point suggestions.

Then last evening, while looking for the components along the Pin 4 circuit for Valve V7A (813), sitting in plain view, was a long thin Panel Strip with four Screw Terminals fitted to it. Stamped into the phenolic board beside each terminal were the numbers 9, 8, 7 and 6 in white paint. My first thought was how odd that they numbered this board backwards. It took a moment or two to sink in the highest number happened to match the highest numbered symbol I had found on the Sender circuit diagram,

So I pulled out the February, 1945 Issue 1 of the Illustrated Parts List and went through the Sender Section looking at all the panels. Eventually, there they were, three of them: 2-Terminal, 3-Terminal and 4-Terminal. All use ANC 8-32 x 5/16-inch binding head Screw Terminals. The challenge was then to find the two smaller ones. Which I eventually did this morning. I will cover them in sequence in separate posts shortly.

One other strong suggestion I have regarding the available 52-Set documentation if you need it to work on a set. Get both the original issue Parts List from 1945 and the revised issue from 1948. In the 1948 version, all the duplicate entries were deleted and the descriptions streamlined. That saved printing costs and reduced the size of the publication, but a lot of useful information was deleted in the process. The 1945 issue listed old and new CMC and ZA Part Numbers. Most old ones were dropped in the 1948 issue. Also, the 1945 version often gave the circuit reference number for parts, like R15A, or C32B, or detailed supporting hardware information. This is largely lost as well in the 1948 version of the Parts List. With this Wireless Set, the more research assets you have on hand, the better.


David

[Bruce Parker (RIP)]

Frikin' amazing Dave.

[David Dunlop]

Of the three of these particular PANELS, this one is the second best hidden on the Sender chassis and I found it when hunting for the components related to Terminal 2. Circuits from V5A, the Master Oscillator/Doubler and V5B, the Amplifier/Doubler are tied into this PANEL. Both of these valves are 6V6G’s.

The three terminals on this panel have their numbers stamped into the phenolic panel and painted white. Terminal 1 is in the upper centre. Terminal 2 is on the lower left and Terminal 3 on the lower right. L33A blocks a good clear view of what is connected to Terminal 1. The CMC Circuit Diagram indicates C27D, the Coupling Capacitor for the V5A Plate, and L32A, the RF Choke for the V5A Plate tie into Terminal 1. Based on the fact the connections for Terminals 2 and 3 on the Circuit Diagram do indeed match what is showing up on these terminals on the actual panel, and that V5A and V5B are giving me no signs of problems so far, I am comfortable assuming all is as it should be with Terminal 1.

Terminal 2 has C11C, the Coupling Capacitor for the V5B Grid, R10A the Parasitic Suppressor for the V5B Grid and L32B the RF Choke for the V5B Grid connected to it.

Terminal 3 is a busy one, being tied to C6C, a Variable Capacitor serving as the V5A Plate Trimmer, C9C, another Variable Capacitor serving for the tuning of the V5A Plate for this valves work as a Doubler. L33A, the 3.5 – 8 MC Tank Coil for the V5A Plate and C28A, the Padder Capacitor, are also associated with this terminal.

The attached photo shows how this PANEL is tucked in behind L33A in the Sender chassis.

My apologies for all the electronic banter in this set of posts. Not knowing yet, how much information is still around in the 52-Set documentation, I thought it might be prudent to put as much information about these three panels down here, while I can, just in case.

One down. Two to go.



David