Wireless Set No. 52 Canadian - Project

[David Dunlop]

Thanks, Bob.

This project certainly generates them.


David

[David Dunlop]

When I recently got the Simpson VTVM, the other half of the equipment ‘give away’ it came with was an older bench Frequency Counter rated to 80 MHz. I haven’t a clue if it will ever be useful in working on either the 19-Sets, or the 52-Set Project, but what the heck...it was free.

It is all solid state, probably late 60’s or 70’s in design, utilizing a probe to connect to the equipment being tested. Currently hunting for documentation to figure out how to use it. From the little reading I have done on these things, direct hookup between the counter and the item being checked would seem to be an advantage because of the ever growing amount of RF pollution these days.

Last weekends rain/snowstorm here, which finally said goodbye last night with a cm dusting of snow, halted 52-Set work. Water got into our basement with enough enthusiasm to get ahead of the sump pump. We had a 2-inch deep 9-foot diameter pool of water that just wicked onto two area rugs and a couple of floor mats before the pump evened the odds. 20 minutes of stability and the pump finally got ahead of the incoming water. Everything is about 90% dry again and back to normal, but we certainly didn’t need the excitement.

David

[James D Teel II]

Our house flooded three times while I was growing up in SW Oklahoma. I can empathize with what you're dealing. I'm glad to see you back on and I pray the damage wasn't too severe.

By the way, I appreciate all the help you've given me with my radio. Check your email for the results.

[David Dunlop]

I am happy to help whenever I can, James.

I was able to get the first set of Sender Resistance Tests reviewed today with my now nicely calibrated RCA VoltOhmyst VTVM, after letting it warm up and stabilize for half an hour.

On the first go back on 10 April 2022, 18 of the 72 tests in this set came back noticeably off specifications and/or ‘odd’. Of those 18 reviewed today, five now came back on specification and the others were noticeably lower in value, or unchanged. So roughly 30% of those 18 readings are now resolved and the rest will need to be investigated.

The Socket for Valve V1J (an ARP-3) has half of its terminals hidden behind the Microphone Transformer T2A, which forms part of the V1J Grid Circuit. For the 10 April 2022 testing, I had chosen to test the V1J Socket terminals from the top, and the probe pins felt a bit too sloppy in the holes, so this time, I decided to remove the T2A Transformer from the lower rear chassis wall of the Sender. This is easily done, as it turns out, by simply removing the two sets of hex nuts and lock washers, as shown in the attached photos. I just let it hang carefully on its leads until the tests were completed from the bottom side of the V1J Socket and then reattached the T2A Transformer to the chassis.

Now onto rechecking the suspicious results for the second test.


David

[David Dunlop]

It was a stressful, but productive evening yesterday. I ended up spending it with my ears tuned to the sump pump in the furnace room, listening to hear if it would kick in, while my eyes were on my VTVM, getting the testing completed for the second Sender Resistance Tests.

I should take the time here to clarify a few points. All three resistance tests require the valves to be removed from the Sender chassis. The first test was a basic pin by pin check from each valve socket to ground, with, from time to time, the Mode of Operation Switch and the Power Switch in specific positions. This second set of resistance tests is taken from each of the terminals on the two 8-pin Connectors on the upper rear of the Sender, and the 7 terminals on T3A, the Modulation Transformer for the V5D Plate. Again, all readings are to ground and from time to time, the Mode of Operation Switch, Power Switch (and this time) Sender Meter Switch must be in specific positions. A total of 52 tests are involved in this set.

On the first work through, I found 21 results that were suspicious, so last evening, I focused solely on redoing all of these with the VTVM and randomly spot checking a few of the others to see if they were reliable. When all was said and done, two of the 21 tests reexamined now produced good, normal results and are now off the ‘Red Flag List’. For the remainder, all of the ‘Infinity’ readings disappeared and I got good solid resistance values back for my efforts. These are all higher than they should be, and a few are alarmingly so, but it is all data I can work with now.

It is still too early to know exactly what is going on in this Sender, but one interesting observation so far is that when the Mode of Operation Switch is in RT Mode, this seems to produce more than its share of very high readings, when compared to CW, M.C.W. and BREAK IN Modes.

In the meantime, I will try and get the last Sender resistance Test redone today.


David

[David Dunlop]

I finished rechecking the third and final Sender Resistance test this morning. All is now quiet on the Low Pressure Front.

This set of tests involves testing resistance from selected pins on the seven Sender valve sockets to just three terminals on either of the two 8-pin connectors on the back of the Sender. Some of these tests might require specific settings for the Band Selector Switch, Mode of Operation Switch or Power Switch.

22 tests make up this set and in the initial work through, I had 7 suspect results. Of those, three now came out spot on and the remaining four read excessively high, but not as bad as the first round. Interestingly, these four readings all come from the V1J socket for the Voltage Amplifier.

So now that I have believable data, the next step is to look at the actual circuits on the schematics to see what components relate to each test in the three sets of results, and start looking at those parts on an individual basis.


David

[David Dunlop]

I had my fingers crossed there was logic behind the layout of the three sets of resistance tests (there are no guarantees with electronics design) and I was happy to discover the testing sequences in each test indeed follow the Sender Block Diagram, starting at the front end with the Master Oscillator Tuning Circuit built around V5A, a 6V6G. They then added in V6A (the VR 150 Voltage Regulator) following into the Amplifiers V5B and V5C and arriving at V7A (the impressive 813 Power Amplifier). Testing then moved to the Audio Input Circuit V1J (ARP-3) and V5D, which ultimately end up at V7A as well.

Starting with the first test set, the first thing I noticed was I had good results through the first four blocks of the Sender (V5A, V6A, V5B and V5C) with the exception of Pin 1 on V5A, V5B and V5C.

A quick look at results on the third test set showed good results across all these valves as well. The problem showing up with the results on Pin 1 was that each test to ground should have produced a reading of 1 meg worth of Ohms. My readings were 1.50 meg taken from the top of the sockets; a little too high for my liking. From the bottom side of the chassis, access to the V5A socket is completely blocked and parts of the other three are tricky to get at as well. The real annoyance, however, was that Pin 1 on all of these valves is an open pin, never used by the valves and the designers take advantage of this feature to use the Pin 1 terminal on the socket as a connection tag to solder leads and wires from other components to, in order to complete other, often unrelated circuits. The issue with this is that when you look at the circuit schematics for any one of these valves, connections to Pin 1 do not show up. They are blank. The only way to find out what is connected to them is to actually look very carefully at the actual terminals on the sockets and hope the connections can be easily traced to identifiable components.

So before being able to dig any deeper into the resistance test results, I needed to get a better look at what was going on underneath the V5A socket. The attached photo shows what this section of the chassis looks like from the bottom, covered with a heavy metal plate with the Modification Card Holder mounted to it.

David