Wireless Set No. 52 Canadian - Project

[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

[Bruce MacMillan]

Originally Posted by David Dunlop

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

Keep it up, more is better than less. I assume all this info will be in the definitive 52 set restoration guide when you publish it!

[David Dunlop]

Thanks for your comments Bruce. This project has some alarmingly slow moments so I am not certain if the publication you suggest will be doable once this 52-Set is finished and back on the air. Even factoring in the philosophical question as to whether or not any project is ever truly finished.

Not only is this the smallest of these three PANELS, it is the most miserably hidden on the Sender Chassis.

As noted in my earlier post of the illustrations of the three PANELS, if looked at right side up, the left side Screw Terminal has a white ‘5’ stamped into the panel to the upper right of the terminal. The right side Screw Terminal has the white ‘4’ stamped into the panel at the lower left of the terminal. Are you confused yet?

This small panel is located in the bottom front left corner of the Sender Chassis, just above the bank of three coils, L35A, L33B and L36A. You will first notice the wafers of the R.F. Driver Band Change Switch, S13A, and then catch sight of this panel tucked well in behind it.

According to the Sender Circuit Diagram, Terminal 4 links between C27E, the V5B Plate Coupling Capacitor and Switch S13A. In turn, Terminal 5 joins Switch S13A to C8E, the V5C Grid Coupling Capacitor, R10B the V5C Grid Parasitic Suppressor and Pin 5 Grid 1 Circuit of V5C (6V6G) the Intermediate Power Amplifier. I can make out R10B coming off Pin 5 of the V5C socket and going to Pin 1, which is being used as a connection tag, and that is pretty much it for certain, without a major disassembly being undertaken. Once again, I am assuming all is correct and OK with these circuits as I am getting good, normal test results from V5B and V5C so far.

The attached photo gives you an idea of how nicely hidden this panel is on the Sender chassis. You can see the screw of Terminal 5 to the left, the two smaller, round head mounting screws, one above the other in the middle of the panel and just make out part of the Terminal 4 screw peeking out on the right.

One left to go.


David

[David Dunlop]

As I noted back in Post #859, it took a little while to ‘connect the dots’ between the strange set of nine numbered symbols I had first noticed on the Sender Circuit Diagram on Page 203 of the 52-Set Operators Manual, and the actual hardware mounted in the Sender chassis. It was this particular panel, hiding in plain sight, that I finally saw for the first time and allowed me to understand the symbols. The attached photo clearly shows how obvious this panel actually is, if ones eyes are truly open.

I still do not know why these four terminals had to be numbered in reverse order, but they were. This photo also shows the stamped numbers in the phenolic panel very well (common to all three such panels) as well as how the ring terminals and sleeves are set up on the wires connected to the terminals. This feature is also common to all three panels.

Terminal 6 is set up between S13A and C8D, the Grid Coupling Capacitor for V7A (813), L34B, the V7A Grid RF Choke, C26G, the V7A Grid RF Bypass Capacitor and S16A, the Mode of Operation Switch. Also tied into it is R8A, the Parasitic Suppressor feeding to Pin 4 (Grid No. 1) on V7A. This all caught my attention since the Pin 4 circuits are giving me the bulk of the bad readings for V7A at the moment.

Terminal 7 is between S13A and C27F on Pin 3 of V5C, the Plate Coupling Capacitor, L43A, the V5C Grid 7 – 16 MC Tank Coil, and C17A, the variable V5C Plate Tuning Capacitor.

Terminal 8 is between S13A and L34C, the V5C Grid RF Choke, C27F on Pin 3 of V5C, the Plate Coupling Capacitor, and R39C, the V5C Screen Voltage Dropping Resister, and R7E, the V5C Screen Parasitic Suppressor on Pin 4 of V5C.

Terminal 9 is the last of this series of screw terminals. It is situated between S13A and R57A and R57B, a series set of 600,000 Ohm HT Metering Resisters, and C26H, the V7A Screen RF Bypass Capacitor connected to Pin 3 (Grid No. 2) on V7A. This circuit is now also of interest since the meter reading for the Sender HT Circuit was only giving me 110 Volts DC (+/-) when the Supply Unit was running, and the actual readings should be either 300, or 600 Volts DC, dependant on whether one, or both of the Supply Unit Dynamotors are running.
So it looks like the time it took to trace out what these nine terminals are doing in the Sender was a worthwhile effort as it gave me a better focus on where two of the major problems with the Sender circuits might be located.

David