Wireless Set No. 52 Canadian - Project

[David Dunlop]

Another good weekend for slowly moving forward with this project.

I started early Saturday morning with a quick trip to the local Canadian Tire Store to obtain some information. As I suspected, they do not do ‘inter-store transfers of products’ due to the fact all stores are privately owned franchises. They also do not ship out of province from any store apparently, to keep the paperwork simple. So that ruled out any easy way of getting more ‘Gloss Navy Grey’ spray paint, if I needed to do so.

Back home, I took a deep breath and set up to get the Covers and Knobs, Metal for the Supply Unit finish coat painted. Happily, everything went smoothly and they will be ready to temporarily reinstall on the Supply Unit at the end of the month.

In the meantime, I have to dive back into Ohm’s Law and see what calculations I can come up with to get the testing completed on the power output of the Sender section of the Supply Unit.


David

[David Dunlop]

While all things ‘Gloss Navy Grey’ were swimming through my head the other day, I made an interesting discovery with the 52-Set that I had completely missed up until now. The one other part of the set which was painted Gloss Navy Grey and which would never have received a coat of varnish, is the SCREENS, Metal, Perforated that protects the front of the loudspeaker in the Receiver.

I only noticed this while looking at my Remote Receiver, which is all original, except for the new Tuning Dial Plate that was installed at some point in its service life, and the addition of the white decal under the Meter stating this replacement dial is ‘None Luminous’. While looking at the decal, I suddenly noticed the Screens assembly was the same grey as the Knobs, Metal on the receiver. A quick look at the Main Set Receiver, which had some Shop work done on it at one point, and I noticed its Screens had received a coat of varnish and was showing the typical patina that developed over time.


David

[David Dunlop]

Work is still plodding along with the Supply Unit in a number of areas. The Covers and Knobs, Metal are curing quietly away until the end of the month, when they can be reinstalled and I have been working on two other objectives in the interim.

The first item I have been struggling with is the output capability of the two Rotary Transformers (Dynamotors), MG1A HP and MG2A HP in the Supply. The MG1A HP unit I am comfortable working with as its output is well within the testing limit of all my available test equipment, which has an effective DC Voltage limit of 1,000 volts. The MG2A HP unit, however, is a different animal entirely, for which I had to dust off my math skills to really understand it. So if you are ready for some really boring trivia, here goes.

The information Robbins & Myers provided on their data plates for the two rotary transformers is as follows:

MG1A HP:

Input: 11 Volts @ 8.5 Amps
Output: 285 Volts @ .15 Amps

MG2A HP:

Input: 11 Volts @ 25 Amps
Output: 1,300 Volts @ .12 Amps

These values would have been obtained under a full load test and I am assuming that since these two rotary transformers were the upgraded ones produced in 1945, the load would have been the Sender Unit of a complete 52-Set very likely provided to Robbins & Myers by Canadian Marconi for the purposes of developing the new dynamotors. What really caught my eye was the input voltage used by Robbins & Myers was only 11 Volts DC. Then I remembered a cautionary note in the 52-Set Operator’s Manual advising that once the sets wireless batteries reached 10.5 Volts DC, they must be replaced with fresh batteries and recharged immediately, because the performance of the 52-Set will be compromised otherwise. So Robbins & Myers probably set 11 Volts DC as the lowest effective voltage to test the dynamotor performance against.

While trying to glean as much useful information as possible out of the Overhaul Manual for the 52-Set, I found a reference to the output voltages for the two rotary transformers from Canadian Marconi’s testing.

“The output voltages of the supply unit shall be within the following limits with an input voltage of 12 Volts measured at the terminals of the supply unit end with full load on the output circuit:

MG1A supply: 300 Volts +/- 10% at 175 mA.

MG2A supply: 1,430 Volts +/- 10% at 120 mA.

End Quote.

Again, from the Operator’s Manual, the optimum voltage from the wireless batteries is noted at 12.5 Volts DC, and that value pops up from time to time in the manual, but 12 Volts DC is the normally expected operating voltage for the 52-Set. So Canadian Marconi used 12 Volts DC for their testing.

When you look at the DC Voltage increase between the two tests, you get an upgrade of 7.09%. The increase in output for the MG1A dynamotor comes out at 7.5% and the similar calculation of the MG2A output gives us a 10% increase. So a 1 Volt DC input increase produces a close similar percentage increase on output.

Where things got really interesting was a later comment on the Overhaul Manual from Canadian Marconi:

“The voltage regulation of the supply unit from full load to no load on the output circuits shall not be more than the following:

MG1A Dynamotor 35% at 175 mA.

MG2A Dynamotor 40% at 120 mA.

End Quote.

So if the Supply Unit of the 52-Set is in a stand-alone mode on the bench being tested, as mine will be at the moment, the “no load” output of the two dynamotors will be in the area of:

MG1A 405 Volts DC

MG2A 2,002 Volts DC



So the MG1A HP unit is well within the safe test range of my available multimeters, but MG2A is alarmingly over this limit. On the bright side, back when I was restoring the ZE-11 Remote Supply for the Remote Receiver, I had to but some 10-Watt Resistors to fabricate the correct test load. I think I have 4 x 8.2K Ohm and a pair of 3.3K Ohm ones tucked away and will have to sort out if that will be enough to get a testable output voltage under the 1,000 Volts DC mark.

Never a dull moment with this project.


David

[David Dunlop]

The other little bit of work on the Supply Unit at the moment centres on the Screw-Eye located roughly top centre of the front panel, just above the lamp assembly.

This Screw-Eye was forced closed by a blow from something, to the point the connector cable from the receiver to the sender would no longer pass through it. The first two photos here show how the two working Screw-Eyes look on the Sender, and how the one for the Supply Unit currently looks.

These Screw-Eyes have a 3/8-inch ID. When I was cleaning up the two for the Sender, I took a tapered punch and slid it into the two Sender Screw-Eyes, marking how far it went with a wrap of masking tape. This gave me a reference for the damaged one from the Supply Unit. The 3rd photo here shows a block of 4 x 4 with a 3/8-inch hole drilled into it, and the punch. The right side of the masking tape is the needed reference line. The 4th photo shows how short the damaged Screw-Eye from the Supply Unit falls from the reference line, when slid down the punch, and the last photo shows how the punch was then used to drift the screw-eye open once more.


David

[David Dunlop]

I am going to use the shank of my 3/8-inch drill bit to reform the damaged Screw-Eye off the Supply Unit. The attached photo shows the start point of the basic concept. I am in no rush and the bulk of reforming the correct circumference of the screw-eye should be relatively straightforward.

Where it is going to get challenging is at the point of closure between the end of the ring, as it gets closer to the shank of the screw. The shank must maintain an orientation of being perpendicular to the circumference of the ring of the Screw-Eye. Or to put it another way, the shank of the screw must point to the centre of the eye when I am finished.

David

[Bruce MacMillan]

Originally Posted by David Dunlop

So the MG1A HP unit is well within the safe test range of my available multimeters, but MG2A is alarmingly over this limit. On the bright side, back when I was restoring the ZE-11 Remote Supply for the Remote Receiver, I had to but some 10-Watt Resistors to fabricate the correct test load. I think I have 4 x 8.2K Ohm and a pair of 3.3K Ohm ones tucked away and will have to sort out if that will be enough to get a testable output voltage under the 1,000 Volts DC mark.
Never a dull moment with this project.
David

Another way to measure the voltage is to make a voltage divider with some resistors. Use two equal value resistors in series of high enough value that there is very little current draw, this means they don't have to be high wattage. Measure the voltage drop across each and add together. Dividing the output in two puts the voltage across each to around 1000V. If it is still too high for your meter you can use 3 resisters to get each voltage drop below 1000V.

[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