[TTech]

Just reviewed some of my previous posts and found the photos of the replacement transformers. I can see on the left transformer what looks like a white wire with a red tracer? It's strange but this seems very clear in the photo but not evident when looking at same transformer wires while wearing two pairs of reading glasses. Maybe I should have tried three pairs.

[Chas]

The input primary side:  Red is B+, Blue is Plate.  Output secondary side: Green is Grid and Black is B- or C- or ground...

Established that the primary and secondary are fine by using resistance.

What is supposed to happen is that the primary does not phase shift the secondary. That is one of the reasons for color coding the other to identify primary and secondary start & finish. The reason phase shift must not happen is stray coupling via C- or B+ can feed back audio signals and re-enforce setting up an oscillation.

There is no phase shift normally for this installation....

If you want to know if the phase is correct. You will need an audio generator that can be set for 2khz and variable voltage from .25 to 5 volts.

Need a carbon resistor of somewhere from 10K to 50k 1/4 W.

Two channels of the scope, set to display 4 cycles of the 2khz., +trigger on ch1 set at .1 volt., no storage.

Move trace 1 to upper area and trace two to lower.

Remove any connections to the A-K at the batteries, remove the detector and the two audio tubes.

I tried to work out not disconnection the transformers, but it will be better to disconnect the transformers.

Take one primary lead and one secondary lead (the current plate and grid wires) ti the primary connect the resistor, the resistor to the generator signal lead. Connect the common grounds to the B- of the transformer and the C- of the transformer.

Connect ch1 to the plate lead where the resistor is and connect Ch2 to the grid lead. The scope should see the transformer with no resistors. The resistor is to isolate the impedance of the generator.

Now jump the common ground lead to C- of the transformer. Bring up the generator to one volt by viewing the scope, be sure the trigger is coupled to channel one so it takes off at the same time. You should see channel 1 and two in phase. Both rising/falling in step, OR falling depending if (-) trigger was selected and coupled correctly.

If the transformer output is out of phase the signal will be 180 degrees out. falling or rising opposite of the other.

You will have to adjust the amplitude of the secondary..

Set the generator to create an envelope of one division on channel one. set channel two to the same division. The resultant signal on the wave form will be the amount of voltage gain from the transformer.

I think you will see at least 3:1 but could be as much as 5:1. If you change the frequency to say 1khz the ratio may change, will be lower ratio at 440hz. This is the "roll-off" of the transformer.

If the signal is in phase then simply re-solder the connections. If it is not reverse either the pair of primaries or the pair of secondaries, not both. That will correct the phase.

Do both transformers as the colors were lost on each.

The radio should function normally, with in phase connections.

If the radio howls either there is a phase mistake or the radio requires that one of the transformers has to invert the phase.

If that is so, then select either transformer that has long enough wires to swap just one pair of wires. on one winding. Do not swap twice...

If you note that at 2khz one transformer has a higher ratio than the other it would be best to place that transformer as the first audio transformer, the volume will of the detector will be improved when used for DX.

The cotton braided wire covering is a solid color coded, no tracer, but the asphalt potting stains it badly very difficult to see the color even if using a solvent to wash out the tar.

GL   Chas

[TTech]

Thanks Chas,

No worry on me cross connecting B+. Or for the most part anything else. The Rocket Science was not helpful and perhaps misguided. My forty years in electronics is in ground based aircraft guidance and communication. As well as 3-phase power systems and battery backup. With deadly voltages, current and phases, with very harmful high levels of RF in some of the guidance equipment. For me the most complex was the ILS  cat-3 mark20 capture effect glide slope and localizer. Their purpose, with the pilots hands off the controls, landing the aircraft in at worst, zero visibility.

I make that statement to somewhat identify myself and my abilities. I am not a Rocket Scientist, or an Engineer. But I was a sharp enough Tech to help engineers develop detailed alignment procedures for complex tower communication systems once installed. Even was taxed with developing an Order/ Book, giving various contractors that build aircraft ground based aircraft systems, needed standardization of screen data used to maintain equipment. It was approved, printed, and distributed nationwide. As a matter of fact if any of you have worked on the Mark 20 ILS systems. The various screens you pull up for trouble shooting or maintenance, was designed by myself and used by the contractor building the software display, following the guidance provided in previously mentioned order.

I make that statement to defend myself. When I come in contact with anyone for the first time, I give them the benefit of  knowing more than me.
Even with the equipment I was considered an expert in. Can I be as dense as an oak tree, sure can. Was trained in solid state and digital equipment to include radio transmitters and receivers. Find it's a whole different world applying what I know and am familiar with to the technology of 1924. With this radio learned they didn't even list the station frequency, but do list it's wavelength.

Thanks for the detailed instructions. That is all very very helpful and will help me reach my final goal. But if I am expected to endure being a creature labeled as less than capable and totally clueless, forever. It's time for me to move on.

Sometimes wish I could take people into the equipment buildings that were my home for many years. Have the equipment inop with missing parts and then be critical of them because they don't know how to build a new VOR bridge network. Or by not having the faintest idea what it means or what to do if flight check tells you your localizer checks 5 DDM to the right.

Thanks

Tim

[Chas]

For sure it is the technicians who build/test the product and for the most part take the risks... Your good to go with the A-K 20... chas

[TTech]

Waiting on the ARBE-III to arrive. Would like to pursue another topic while waiting. Started this thread with pic's and questions to hopefully build a bit of foundation for the next (NEW) person with an Atwater Kent model 20 Big Box. While attempting to research online found that critical information in older posts were no longer available because info or pic's were not posted in the thread. When folks were kind enough to respond they listed a web site where wanted info could be found. It's the referred web site locations that fall through over time. Web site closing, purging of data,etc. leaves large gaps in wanted information. Wanted to develop a post with all info, guidance, mistakes, successes, failures, with pic's to be of help for years down the road when the next person finds an A.K.  Model 20 Big Box. What an exciting find.    

Recently received a reply with long awaited info, but it came at a cost. The cost was ridicule, chastisement and such distain in replying to my question the "ahem" gentleman felt a need to apologize to the forum readers for my inability to..... so many words could fill the blanks. 

So if I could be so bold I would like to take the liberty to make a statement and preform another disdained action. Ask another question.

Statement: Of course I welcome all knowledge, suggestions, corrections and, unacceptable as it has become, encouragement. The replies I received from ELLOT NESS, Mikethedruid, and Phlogiston are most informative, and helpful. Just good old fashioned helpful and friendly. I'm 64 years of age and have not lived a sheltered life. Feel free to respond any way you want. But if it's not  at least with the spirit of helpfulness and respect, in my little world, you just don't count. Maybe my intentions are flawed. I am capable of repairing the radio on my own with no assistance or help. Was just wanting some company along the way. Save a little time, increase my knowledge beyond just fixing the radio. And maybe help someone else. And who know's, have a little fun.

Question: Is anyone interested in this post for the reason I started it? Over 1600 have viewed, but I don't know why they did so. Is it to learn and enjoy someone else's project, Or some other reason.     

Thanks

Tim

[admin]

From a board administrator.

This has been, up until Page 4, a quite interesting thread. Please, people, let's not go off the rails now.

Tim, I think you misunderstood Chas' intent - I read his posts as only being helpful, or trying to be so. (reference post #47 above and the reply in post #48)

It isn't always easy to see helpfulness, or attempts at humor, etc., etc. in a typed forum where we are not communicating face to face, or at least in real time via Zoom or other online chat. Misunderstandings often occur. I'm asking everyone to please keep that in mind, and also to please keep an open mind when posting and/or replying here.

Everyone - be mindful of the Phorum Rules, please, and play nice.

Carry on...

[Ron Ramirez]

I own a 20 Big Box and have been reading with interest, although I have not commented/contributed until now.

In other words - 

My 20 Big Box will require restoration, and so I've been watching, taking it all in... So to answer the question - Yes, I'm interested. And I'm sure others are as well.

I hope this thread can continue and become a repository of information for the future, and not go off the rails as the admin said above.

[mikethedruid]

TTech, I appreciate your thread and its purpose. Don't let yourself be discouraged.

[Phlogiston]

I don't have a "big box" 20. I do have the smaller one - 20C, I think. It is the only 3-dialer, on display, that has a dedicated power supply. I demo it for people, but, the more common use is to test 201, 201A, 200 and 200A tubes ( and their variations ). This helps me escape the "can't test a gas detector " syndrome. The power supply is fully variable so that detector voltages (as with all B+, A+ and C-) can be adjusted to find the sweet spot for best operation. Since the detector position is designed for a 1 amp tube 201s can work there - usually poorly.

Russ

P.S. Speaking of power supplies - I added plate chokes to all of the B+ outputs on this power supply eliminating any residual inverter hum:

https://www.russoldradios.com/blog/more-...ered-radio

This is not the supply running the 20C. It is a "bruit-force" unit, capable of handling tubes that fail.

- and - If you think about it, many of AKs "metal box" radios are so very similar to the 20©. Like the 40 - very common, it is basically the same circuit as the 20 with an AC supply built in and 226 tubes which are just a 201 with a heavy (important) 1.5 volt filament and improved output tubes and speaker.

[mikethedruid]

Russ, I have an A-K 40, it was one of the first radios in my collection. I bought it at the Salvation Army when I was a kid for 3 dollars, since it does not have its own speaker and they couldn't test it. I rigged it up with a speaker with an output transformer from a radio I had torn apart, and, lo and behold, it worked ! Later I got an RCA model 100-A speaker and used that with it.

[Ron Ramirez]

One of the first radios I bought, about 400 years ago, was an AK 20 Compact (7570). I brought it back to life and was amazed how such a primitive instrument could bring in so many stations.

I bid on, and lost, an AK 20 Big Box with an AK horn speaker a few years later at a local auction. This is why I have the 20 Big Box I have now, plus this one was cheap at a local swap meet. I remembered the one I lost out on and bought this one for $20.

[mikethedruid]

TTech, several months ago I got a binder of Atwater-Kent service literature on eBay. It is missing some things, including the actual service pages for the model 20, but it does contain some pages you may find useful in the earliest parts catalog. I have also included the pages for the A-K model 20 variations from my Rider's.

[Image: https://64.media.tumblr.com/9f8b55a3d09e...d0e1cf.jpg]

[Image: https://64.media.tumblr.com/df5d3d93b840...180caf.jpg]

[Image: https://64.media.tumblr.com/42b4ed6fdc76...40bc8f.jpg]

[Image: https://64.media.tumblr.com/546280c98120...25f49c.jpg]

[Image: https://64.media.tumblr.com/39b6d9ee16d4...bd7f31.jpg]

[Image: https://64.media.tumblr.com/c0c05f029370...217d8e.jpg]
[Image: https://64.media.tumblr.com/ddeb6cc2d1e0...42a4a0.jpg]

[TTech]

Enjoyed the helpful radio information, radio suggestions, and sharing of past radios and history. The original service literature was a bonus. Great to see the information and data in such clear and pristine condition. Received the ARBE-III late today, just enough time to unpack it and check it out. Neat fairly compact unit with many outputs that will let me start all fed voltages to the radio at much lower levels. Then continue to increase voltages if all continues to function normally. Made very basic first checks on the radio by simply using  a 9 volt battery, tubes removed. Checked for voltage at filament contact points for each tube. Including input and output from each transformer. Also injected  modulated rf at antenna input and checked for modulated rf at points through out the radio, tubes installed, once again testing for continuity through wiring and transformers. So far no sign of opens, shorts, or dirty rheostats. Have found one open resistor, replaced two caps. Both rheostats and the antenna tap were so dirty they for the most part tested open. Pull up on the metal slotted brass tab and pull off rheostat knob, all is easy to clean. Hopefully I'll be able to spend some more time with it this week end.

[Chas]

Tim,
The ARBE web site has a list of 20's sets and how to connect them to their product. The A-K 20 is on that list
Chas

[OZ4]

It sounds like you have been red pilled. Welcome to reality.

After reading more I don't quite understand what happened here.

Now I think my comment is not appropriate.