Wireless Set No. 52 Canadian - Project

[Chris Suslowicz]

Bear in mind that resistors have a voltage rating too, and that high value low wattage resistors may flash over rather than burn out if the voltage rating is exceeded. For high wattage resistors you can assume the voltage rating is adequate for the full power rating, so voltage = square root of (resistance value x power rating).

For your 8.2k 10W resistors that's 286 volts and with 4 in series = 1145 volts which should be fine.

Using them all in series as a test load and with a suitably high resistance multimeter (20k ohms per volt), you should have no problem measuring the output voltage on a 40 watt (approximately) load by using the meter between ground and the 'hot' end of the lowest resistor in the chain. (I'd suggest starting on the 1,000 volt range of the meter first, just in case.)

Then multiply the meter reading by 4 to get the actual (approximate because the resistor could be only within 20% of its marked value) voltage.

Alternatively, you can put the meter in series with all the resistors and measure the current through the chain - put the meter between ground and the lowest resistor and don't touch it when the power is on (if the meter is open circuit parts of it will be at full HT voltage and that is definitely lethal) - then multiply total resistance by current drawn to get the applied voltage.

Chris

[David Dunlop]

Bruce and Chris.

Thank you both for the comments. You have confirmed I am on the right track.

I have found with this project that there are not nearly enough opportunities so far to actually work with the various equations and formula used with electronics work. The gaps between usage are so great I forget a lot of the details and then spend a lot of time having to refresh my mind on how they all work. Your assistance is much appreciated.

So far, my calculations suggest I am going to be dealing with about 4+ Watts, testing the dynamotors, and the one rule I am going to be focusing real hard on when the time comes, is 'Keep my left hand on my lap at all times!' .


David

[David Dunlop]

Fun day today! Sitting inside watching the 3rd blizzard in a week roll into town.

I have been able to do some more work on restoring the Screw-Eyes, 4-40 for the top of the Supply Unit front panel. The circumference of the eye is now true, but the gap at the shank still needs to be closed up. It currently sits at about 3/32-inch wide, which is just enough for the lock washer to slide all the way around the body of the screw-eye.

The more I look at it, I am thinking that if I can close the gap up properly, the longitudinal axis of the shank should automatically end up pointing directly at the centre of the eye, so I might get a break there.

A couple of before and after photos posted today of the work so far.


David

[David Dunlop]

I was mulling over how to close up the final gap in the Screw-Eyes assembly for the Supply Unit without compromising the uniformity of the circumference of the eye and a pair of pliers on my bench caught my eye.

A lot of pliers have a built in cutter between the jaws and the pivot point of the handles. The backside of the cutters is typically cut away in a circle, the diameter of which varies to some degree. I rummaged in the tool chest and found my Dad’s old black handle pliers and this cutter hole was just the right fit to carefully close up the gap in the Screw-Eye.

This screw-eye now matches the gaps in the two on the Sender and the lock washer stays put once slipped onto the shank and the hex nut installed. Last photo today shows the Supply Unit Screw-Eyes all polished up with the pin terminal of the connector for the receiver sitting nicely inside the Screw-Eye. The free play inside the eye matches that in the two screw-eyes on the Sender.

A little more progress accomplished. I might just celebrate by shovelling the snow off the front walk from yesterday’s blizzard.


David

[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