Wireless Set No. 52 Canadian - Project

[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

[David Dunlop]

Just a quick look at the set now with the semi-restored Supply Unit temporarily reinstalled in the Carriers No. 4.

Also a close-up of the Screw-Eyes restored and functioning as originally intended at the top of the Supply Unit. With the Connector Cable now able to run through the Screw-Eyes instead of over/around it, it has about one-half inch more free play in it and now looks just as relaxed in place as these connectors do in the surviving wartime photographs.


David

[David Dunlop]

As I have mentioned before, working with the surviving documentation for the Wireless Set No. 52 is a real challenge for a whole host of reasons, but it is what it is. You just have to read through every document you have, frequently several times, to locate all the information available for any given topic, and then make the best sense of it you can.

A good example recently surfaced regarding the Brushes in the two Dynamotors. Most of the available information regarding the inspection and maintenance of these items states the eight brushes should be inspected monthly for damage and wear. They should be carefully removed from their holders, checked and put back exactly as they came out. New ones must be worked in with an hours run time under no load. None of the information I had found to date advised how to access all the Brush Holders in situ, and the removal of the actual Dynamotors from the Supply Unit for servicing covered only the upper one (MG1A).

Not sure how I missed it up until now, but I was looking through the Working Instructions last evening and discovered a little table tucked away near the back of it explaining how to inspect each of the eight brushes when the Supply Unit is out of the Carriers No. 4, which was a very nice find. It also mentioned it is not necessary to completely remove the brushes from their holders to inspect them.

I posted the page here for future reference.


David

[David Dunlop]

Slow and steady still with this project, focusing primarily on ensuring the Supply Unit is in good order before going back to the Sender.

I have now confirmed the oddball reading of just over 70 Ohms I got on one of the Supply Unit Resistance tests relates to a pair of 300 Ohm 1/2-Watt resistors set up in two parallel feeds in the Vibrator circuit for the Receiver Supply. This parallel arrangement of the two 300 Ohm resistors should produce a resistance value of exactly one half the rated value of either resistor, or 150 Ohms. So one, or both, of those two resistors has dropped significantly off specifications. Confirming test yet to be done.

I spent a chunk of yesterday afternoon searching the web for a supply of 300 Ohm, 1/2-Watt Carbon Composite resistors, which proved a bit of a challenge. Current standards now bracket that Ohms value by about 20 Ohms either side. I did, however, eventually find a supplier with 300 Ohm 1-Watt carbon composites which will work nicely, so will be ordering 10 for the project. That will give me a chance to match a pair for this fix and leave me spares for the rest of the project, if needed. The two in the Supply Unit are R13D and E, so at least three others are in the 52-Set in other locations.

When I had reinstalled the Supply Unit in the Carriers No. 4 to allow for the Isolation Relay to be tested in the Sender, I had the meter set up to monitor the Sender data. Last evening, I fired up the Receiver to see how the signal from WWV at 10.0 MC was behaving, so I had switched the meter back to monitor the Receiver. I was very surprised, and pleased, to see the LT was reading a rock steady 11.25 Volts DC and the HT a rock steady 155 Volts DC. Checked again this morning and same results. They are no longer wandering all over the dial, as low as 10 Volts LT and 120 Volts HT. What I find odd is I have yet to do any electronic adjustments or repairs to the Supply Unit that may have caused this to happen. I still intend to more closely examine the Connector assembly between all five 8-Pin Connectors across the set, but another related possibility is oxide buildup on all those contacts, so I shall add cleaning all the related sockets and plugs with Deoxit just to be sure.

I have also noted that when the time comes for hot testing the Sender, it needs to be done at High Power. I am glad I picked up the extra CPP-2 Power Supply from Brian Asbury last year. It is soon to come in real handy.

David