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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Nov Tue 08, 2016 3:33 am 
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Location: Brigus NL Canada
I came up with a somewhat similar setup that worked very well for me. But first I have to repeat the earlier cautions about the very real shock hazard here. If you're working with 120v AC, reduce the danger by using an isolation transformer!
In my projects I used a cheap plastic cutting board from the Dollar Store as my circuit breadboard. Mounting (and changing) the components was very simple. I used short round head wood screws and washers as terminals to connect and clamp down the leads from resistors and capacitors, etc. no solder needed. Drilling a small pilot hole for each screw makes it easy, and components can be added or changed very easily. I mounted tube sockets face-up with longer screws through bits of plastic tubing as standoffs under the mounting holes. (You will need solder for connections here, but you can run short wire leads to wood screw terminals around the socket to maintain the ease of changing ore adding components.) Just remember the socket pin numbering will be the reverse of the usual method we use where we wire the socket from the underside!
The plastic cutting board takes wood screws very nicely, and is a good insulator.
I made a couple of 1-tube and 2-tube transmitters this way. Sorry I don't have any photos.
Dave M
NL, Canada


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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Nov Fri 11, 2016 3:13 am 
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Location: Groveland MA
Well, the more I thought about things, the more I liked the idea of using relay bases. As luck would have it, I was able to source the relay bases and some terminal blocks from work.
Thanks for the idea Sal!

I have swapped out the tube sockets, next step is to build the oscillator circuit.

Russ


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File comment: Relay bases installed.
RT_R4 copy.jpg
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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Nov Sun 27, 2016 8:08 pm 
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A little more progress, I have added some components, and have done some experiments with tubes. Not quite ready to build an operating circuit, still have more tests to do.

Russ


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RT_Radio.jpg
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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Nov Sun 27, 2016 10:48 pm 
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It's coming along very nicely.

So... who are your intended student trainees going to be? Where are they going to come from?
Do you teach a basic radio class regularly now somewhere?

BTW:
I see that the IF cans you've chosen are the troublesome type prone to Silver Mica Disease.
Have you checked them or updated the caps inside?

If you find a seriously bad one... it may be a good idea not to fix it and keep it as a test unit to use when training.
Connect it and let the student learn to identify the noise and and detect it.

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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Nov Tue 29, 2016 4:02 am 
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Pbpix wrote:
It's coming along very nicely.

So... who are your intended student trainees going to be? Where are they going to come from?
Do you teach a basic radio class regularly now somewhere?


Thanks! Actually, I am the student, this is to help me better understand things.

Pbpix wrote:
BTW:
I see that the IF cans you've chosen are the troublesome type prone to Silver Mica Disease.
Have you checked them or updated the caps inside?

If you find a seriously bad one... it may be a good idea not to fix it and keep it as a test unit to use when training.
Connect it and let the student learn to identify the noise and and detect it.


At this point, I have only checked the continuity of the coils. Today I connected the oscillator circuit, but not the first IF and was able to see the oscillator running. It will be interesting to see what happens once I connect the IF. I recently ordered some caps to install in the cans, so I can make the repair if necessary. I may go ahead and replace the caps even if the existing ones are OK so that I have had some practice for when I am working on a real radio.

Russ

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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Dec Sat 17, 2016 2:50 pm 
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Making a bit of progress here. I have it almost working, I can pick up a signal from my AM transmitter, but not any real stations yet. The original speaker that was mounted turned out to bad, although I am sure that I tested it before installing it. In any case in this photo I am temporarily connected to a speaker in a parts radio. I also swapped out the tuning cap, the one that I had from a DTI trainer had tuning caps of equal size (capacatance) which was not really suitable for the oscillator circuit.

Russ


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RT_R5.jpg
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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Dec Sat 17, 2016 3:52 pm 
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I would suggest a flat metal plate in front of the capacitor and connect the shaft with an insulated coupler to avoid hand capacitance. I have several spare couplers that work with .25" shafts. I will donate one to the project if you want it. May even have some large plastic knobs hanging around. They help isolate you from the capacitor also. If you want to get fancy there are couplers with gear reduction and isolation out there. Eliminates the need for dial cord. Nice looking work.

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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Dec Sat 17, 2016 5:36 pm 
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Thanks Rick, I will see what I can dig up for the tuning cap, I should have something to insulate it. Touching it definitely causes tuning issues :D
Waving my hand (but not touching) over various areas of the radio also produces changes in sound. Maybe that is how they figured out how to make a theremin :wink:

Russ

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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Dec Sat 17, 2016 8:04 pm 
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If you aren't getting any stations, I would first verify that the oscillator is working. Do the second radio test for that.

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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Dec Sun 18, 2016 12:11 am 
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Rick, found a knob, so I am all set. Thanks very much for your offer though.
Fifties, I did not think to mention it, but my oscillator is working, though I am sure it is not the best.

I added a ground to the metal plate that holds the on/off volume control to help reduce noise. I am currently able to get one local station, and can hear some other places on the dial where there might be something.

Russ

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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Dec Sun 18, 2016 12:49 am 
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If you are getting stations then the oscillator is working.

You might try rotating your air loop when tuned to a weak signal, also if you have other loops try them all to see which might match up best.

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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Dec Sun 18, 2016 1:52 am 
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radioalfa wrote:
..., the one that I had from a DTI trainer had tuning caps of equal size (capacatance) which was not really suitable for the oscillator circuit.

Russ
This was very common. It's handled by trimmer (in parallel with the tuning) and padder (in series with the tuning) caps.


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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Dec Sun 18, 2016 2:59 am 
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black85vette wrote:
I would suggest a flat metal plate in front of the capacitor and connect the shaft with an insulated coupler to avoid hand capacitance.

Or possibly silicone a plastic jar lid.
Image
Looks like a really fun project. Nice work.


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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Dec Sun 18, 2016 5:43 am 
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If the capacitor frame is grounded I don't see why hand capacitance would be an issue unless it is due to the design.


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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Dec Sat 31, 2016 5:00 pm 
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A lot of changes since the last time.

-Moved the tuning cap and oscillator coil closer to the 12SA7 to shorten the wires that connect them.
-Changed the common ground by using 14 AWG wire so that I had a better way of connecting to ground (removed the block that I was using for grounds)
-Moved T1 and T2 in between the tubes, again shortening the wires
-Changed the path of the B+line
-Added a resistor and cap to create a "chassis ground" to which I tied pin 1 of each of the first three tubes, the IF cans, and metal bracket that holds the on/off volume control
-Added the resistors for the AVC circuit.
-Made many connections more permanent, eliminating connector blocks.
-Added the antenna to the board.

It is working fairly well, pulling in many stations though to do that I added a 2' wire to the antenna connection and ran it along the front of the radio. With out that wire I only get 3 stations.

Still more experimenting to do, which is the whole point of this :D

Russ


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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Dec Sat 31, 2016 5:52 pm 
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Looking great. I think your changes make sense. Looks like you got the tuning cap isolated with a knob.

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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Dec Sat 31, 2016 9:53 pm 
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Adjusting the antenna trimmer properly on the tuning condenser usually helps optimize signals.

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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Jan Sun 01, 2017 5:05 am 
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Very nice.


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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Jan Sun 01, 2017 8:47 pm 
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Rick, thanks, yes I ended up removing the pulley so that I could move it inward.

Pbpix, thanks I performed an alignment using the procedure in the documentation from the radio that I based it on. I might even swap the tuning cap to experiment, it does seem that something is not quite right.

Tube Radio, thanks!

Russ

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 Post subject: Re: My AA5 Homebrew / Trainer
PostPosted: Jan Sun 01, 2017 8:55 pm 
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radioalfa wrote:
Rick, thanks, yes I ended up removing the pulley so that I could move it inward.

Pbpix, thanks I performed an alignment using the procedure in the documentation from the radio that I based it on. I might even swap the tuning cap to experiment, it does seem that something is not quite right.

Tube Radio, thanks!

Russ

The antenna circuit is a tank circuit based on the cap in the tuner and the inductance of the antenna wire coil. You may have needed to add some wire, as you did, to "trim" the inductance and thereby you may have optimized the tuning

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