Wireless Set No. 52 Canadian - Project

[David Dunlop]

I have now temporarily reinstalled the Covers for the Blower Fan and the Knobs, Metal on the front of the Supply Unit, after repainting them Gloss Navy Grey. It only took two hours to get the four lock washers and hex nuts onto the Covers and lightly secured. Definitely a job best done with the front panel of the Supply Unit off the chassis of the supply. I had to resort to using Debbie’s jewellery pliers and a toothpick to fit the washers on the screw studs, and an assortment of small 5/16-inch drive sockets to get everything back in place. Wonky fingers did not help either.

I will refit the Screw-Eye in the next day or two.

The new paint really stands out against the old, amber tinted varnish on the front panel paint, with all its stains and missing bits, but that garish contrast will tone down a lot when the front panel gets its restoration and repaint. The contrast then should be identical to what took place on the Sender front panel when that work was done. I can at least continue on with the electrical testing of the Supply Unit knowing everything is safe and where it should be for the time being.


David

[David Dunlop]

While I was mucking about with the reinstallation of the Covers assembly for the supply unit Blower Motor today, I made yet another discovery regarding production of the 52-Set.

When I shifted one of my desk lamps to get better illumination of the upper left mounting post of the Covers assembly, the lamp lit up the top of the front end of upper MG1A HP Dynamotor. I had noticed a yellow C-Broad Arrow mark there earlier when looking at the data plate for this dynamotor, but above this stamp I spotted a yellow Philco Stamp and above it a square, yellow, ‘TESTED OK” Stamp. I have run across that latter stamp on a couple of other components of the 52-Set so far, but what intrigued me here was finding further involvement by Philco with production of the 52-Set.

These dynamotors were built by Robbins & Myers, and all produced in 1945. To date, no surviving components of a 52-Set have been found with a production date of 1945. All have been dated in 1944. So the entire production run of 52-Sets, pushing somewhere close to 5,000 sets, probably ended sometime late in 1944 at Canadian Marconi Company, while the contract for upgraded dynamotors for the 52-Set took place in early 1945 at Robbins & Myers. Based on the Philco Test Stamp, is it possible Canadian Marconi was preoccupied with finishing off any wartime contracts it could while also trying to switch gears back into new military or civilian production, possibly also reducing staff, and did not have the capability of testing the replacement dynamotors, so had Philco do it for them?


David

[David Dunlop]

Well I bit the bullet and started the electrical tests of the Supply Unit today. Three of the tests came from the 1st Echelon Maintenance Schedule and confirmed both dynamotors spooled up and the fan circuit remained dormant. That latter test directs the operator to further tests if the fan had activated.

A couple of initial observations were that with both the MG1A and MG2A dynamotors running, and the Supply Unit free standing on the bench, the noise they produced was noticeably less than that created by the 19-Set dynamotor, when that supply is running outside of its case. I was quite impressed about that.

There was a bit of a ‘sandy’ sound coming from the area of the input brushes of MG1A (described as the 11Volt Brushes in the circuit diagrams), so I will check them out once the front panel comes off, because they are hiding right behind it.

I then hooked up my analogue test meter to the MG1A output feed to see just how well this dynamotor was working. At 12 Volt input and under load, the output should be 300 Volts. Under no load at 12 Volts, the regulation of MG1A should not allow it to exceed 35% additional output, or a total output of 405 Volts.

When switched on, it took the meter needle about 1 second to climb from 0 to 300 Volts and another couple of seconds to reach 380 Volts. Two more seconds and the needle stopped one width away from the 400 Volt mark and held there. I am thrilled with those results as my CPP-2 Power Supply was feeding a steady 12.73 Volts DC into the Supply Unit.

Next step will be assembling my string of resistors and seeing what the output of the MG2A dynamotor is doing. In the meantime, I cannot help wondering when the last time was that these two dynamotors were active.


David

[David Dunlop]

It has been a while since my last update, but not much has been done on the project, primarily due to the fact I have not been able to source appropriate resisters needed to determine the output from the MG2A HP Dynamotor in the Supply Unit. Either no stock exists in town for reasonably priced resistors, or they have to be ordered in at ridiculous prices per unit plus shipping. I just cannot justify the expense for a 30 second test and then never use the resistors again.

I did bounce some ideas around with a friend and came up with a simple, quick test I can do using available equipment. It will not give me specific output data, but will tell me if the HP Dynamotor is in good working order, with enough confidence I can continue. Of course, there is still a wrinkle. I will only be able to perform the test when the front panel comes off, as I need access to both Low Tension terminals tucked in behind said panel.

The plan will be to feed 120 Volts AC into the two HT terminals and read the voltage output at the two LT terminals. It should be around the 1.5 Volts AC level if the windings in the Dynamotor are all in good working order. In the meantime, I have been running the Supply Unit on the bench for about 5 minutes a go, every few days and all appears just fine so far.

On a much brighter note, about 10 days ago we bit the bullet and finally bought a brand new 24-inch iMac to replace our original 21-inch from 2006. Been busy setting it up and doing the usual data clean and transfer from the old one. I have also downloaded some design software manuals onto my iPad to read up on. I think one of them may solve all, or most of the problems I have at the moment regarding the ability to design and make water slide transfer decals necessary to restore the front panels on the Supply Unit and Coils, Aerial Tuning assemblies.

So the overall project is still headed in the right direction.


David

[Chris Suslowicz]

Originally Posted by David Dunlop

I did bounce some ideas around with a friend and came up with a simple, quick test I can do using available equipment....

The plan will be to feed 120 Volts AC into the two HT terminals and read the voltage output at the two LT terminals. It should be around the 1.5 Volts AC level if the windings in the Dynamotor are all in good working order.
David

Er... <Mode=HAL> I'm sorry Dave, I'm afraid you can't do that. </Mode>

It's a _rotary_ transformer, which is a DC motor and DC generator sharing a common field winding. It only works in one direction, and then only when it's rotating at the designed speed.

To run it in reverse you would need to separate out the field windings and feed those with 12V DC, feed the output (high voltage) armature winding with high voltage DC (high enough to overcome brush and bearing friction), and measure the voltage across the LT brushes. This is simply not going to work.

If you have had the unit running without excessive current being drawn or smoke/sparks being generated, you can assume it's OK to use - at least for short transmissions.

Best regards,
Chris.

[David Dunlop]

Thanks for the feedback, Chris. Good thing the Drawing Board for this project is huge. The Supply Unit, being the smallest item, and heaviest, is proving to be the most challenging. Very little on it still to be done, can be effectively done without major disassembly rearing its head. Something I really only want to tackle once, things being such a compact fit.

David

[David Dunlop]

When I was working on the Sender, I had taken the testing as far as I could, which was basically up to where a working Supply Unit was needed to feed the Sender for any further testing.

I have gone as far as I can now for the moment with testing the Supply Unit. I completed a set of Resistance Tests this morning. All results were on the mark but one, where I got a 74 Ohm return where there should have been 150 Ohms. I also completed all but one of the Operator’s Maintenance Tests for the Supply Unit. These could be run with the Supply Unit either in, or removed from the Carriers No. 4 and all tests gave positive results. The last test of this group is to turn on the Sender Heaters to let the Sender warm up and then flip the Send/Receive Toggle Switch to ‘SEND’. One should hear the relays in the Sender kick in to isolate the Receiver and both Dynamotors should kick in. A HT1 Voltage reading for the Sender of about 300 Volts DC should also show on the sets meter.

I have a much greater appreciation of why a pair of jumper cables for the 8-Pin Connectors between the Supply Unit and Sender are such a great idea. You can do these tests outside of the Carriers No. 4 with the internals of both the Supply Unit and Sender fully visible. Way too nerve wracking when everything is out of sight.

So back the Supply Unit went into the Carriers No. 4 and everything got reconnected. I turned on the CPP-2 and gave it a 5 minute warmup, and then turned the set on. As soon as the Receiver came on line with the WWV Signal at 10.0 MC, I turned on the Sender Heaters and let the set warm up another 5 minutes. With everything on the Sender roughly tuned into 10.0 MC as well, I then turned on the NET circuit in the Sender. The Dynamotors kicked in nice and quiet, but the HT1 reading for the Sender was only 110 Volts DC, not anywhere near the expected 300 Volt range.

Last critical test was to turn off the NET Switch and flip the last switch on the Supply Unit from RECEIVE to SEND. The isolation relays kicked in perfectly and both Dynamotors wound up, but they were under a very heavy load and very growly. The Sender HT1 Voltage was still no higher than the 110 Volts DC from the previous test so I switched back to RECEIVE right away. So something in the Sender does not want to play well with the other components. Good to know.

Next tests will be to go back to the NET Test and take meter readings for all the Sender valves to see how they compare to the specifications in the manual.


David