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Author Topic: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build  (Read 198302 times)
KB1WSY
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« on: July 07, 2014, 10:08:28 AM »

Greetings all,

Today I'm starting to build "A Simple Two-Tube Transmitter" from the book, "How to Become a Radio Amateur," 1968 edition. This is the companion to "A Three-Transistor Receiver for the Beginner" that I built last summer.

Together, the receiver and transmitter make up a complete Novice station, with a regenerative receiver and crystal-controlled CW transmitter.

The transmitter is QRP, with an input of about 10W which is about 5W output in modern parlance.

Pictures of "Chapter One" of the transmitter project are at the URL below. Further chapters will be posted here as the building proceeds. For the full effect, click on the first photo, then click the "Full Screen" button toward the top left of the screen:

http://tinyurl.com/okzpckr

(Anyone who is interested in the receiver project from last year can find it documented here: http://tinyurl.com/m6tzp8k.)

73 de Martin, KB1WSY
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W7UUU
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« Reply #1 on: July 07, 2014, 10:33:13 AM »

Very cool Martin!  I'll email you with a couple suggestions that might help.
I built much the same as you know but without having seen your exact schematic,
so may not be the case, the one I went from had a couple really wrong part
values and I also found that altering it from a Boosted Pierce to a MOPA got
me a full watt (25% more power!) more output.

I very much look forward to watching this project evolve and hopefully be on the
air soon with your homebrew receiver!

Dave
W7UUU
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My site: www.W7UUU.net - "it's not all about yew, ewe, you!"
KB1WSY
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Posts: 1306




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« Reply #2 on: July 07, 2014, 12:56:34 PM »

The ARRL has given permission for me to reproduce the transmitter's schematic (circuit diagram) in this eham thread. It has now been added to Chapter One linked above -- it's the first picture in the series.

73 de Martin, KB1WSY
« Last Edit: July 07, 2014, 01:52:35 PM by KB1WSY » Logged
WA9CFK
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« Reply #3 on: July 08, 2014, 08:48:08 PM »

Where are you going to get the old style crystals?

What is the modern Crystal equivalent for the old tube rigs?
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G3RZP
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« Reply #4 on: July 09, 2014, 01:26:29 AM »

I think that HC/6U crystals would be OK, but I wouldn't go for anything smaller.
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GW3OQK
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« Reply #5 on: July 09, 2014, 02:26:15 AM »

Martin, I have used the small HC49 crystals which are advertised on ebay for QRP work in a 1950s 50w valve transmitter. The oscillator circuit is a type with crystal between grid and ground so subject to less volts than being between grid and anode. Never a failure  and with a 100 pF trimmer in series with the crystal they have a remarkable couple of kHz pulling range.

I have a tx partly made with a very similar circuit to yours, but no transistors. I have an extra hole in the chassis to add a vfo.

73
Andrew


     
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KB1WSY
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« Reply #6 on: July 09, 2014, 03:59:31 AM »

In response to your comments about crystals: I was very lucky to be able to purchase, from a veteran ham, his collection of FT-243 crystals from the 1940s/50s. These are the "real deal" i.e. they are the robust original crystals, not "retrofitted" thinner modern crystals:



I am aware that this transmitter circuit, sometimes referred to as a "boosted Pierce" oscillator, can be quite tough on the crystals and can even cause them to fracture. However I'm assuming this won't be an issue with the old-fashioned crystals that I will be using.

Today, I am starting on the metalwork. There is quite a lot of preparation needed for this, and I have to be rather careful because there's not much room for error, so I'm not sure when I'll be posting a new "chapter" but it should be within the next day or two.

What is the modern Crystal equivalent for the old tube rigs?

I'm not totally sure I understand your question but there are quite a few modern small QRP transmitters, either assembled or available as kits, that are crystal-controlled. So that would be the modern equivalent I suppose!

73 de Martin, KB1WSY
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KB4QAA
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« Reply #7 on: July 09, 2014, 09:06:50 AM »

Super project, Thanks!
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K8AXW
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« Reply #8 on: July 09, 2014, 09:12:48 AM »

Crystals are designed to work into specific loads (capacitances) and have several other specifications, depending on their use.

Since it has been many decades since I've used crystals so with my FIFO memory that information is long gone.  You need to research the old FT style crystals for the correct operating parameters and then do a search for the modern equivalent.  

At one time any crystal you want could be ordered from a company called International crystal.  I have no idea if they're still in business and this should be researched as well.  

The bottom line is you can't just pop a crystal of a particular frequency into a circuit and expect it to work without being destroyed, having excessive drift as well as other undesirables.

Martin, you should keep and cherish that box of FT crystals!  Would you like to guess how many times I've regretted selling my FT crystals?Huh
« Last Edit: July 09, 2014, 09:15:08 AM by K8AXW » Logged

A Pessimist is Never Disappointed!
WA9CFK
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« Reply #9 on: July 09, 2014, 02:22:56 PM »

I still have my crystals from my novice days but they are all in the phone band now.

I like the idea of resurrecting old Home Brew projects. Building a radio and putting it on the air is what I enjoy most about ham radio. But take warning!! It was very addictive and I could not stop at one. Wink

Now some 50 years later I am still putting the yet another radio on the air and it is just as much fun.

I think I will dig out my copy of "How to Become a Radio Amateur" and prepare for another winter project.
 
Keep us posted on your success.
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G3RZP
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« Reply #10 on: July 09, 2014, 02:37:11 PM »

I doubt very  much that the circuit ever would damage the FT243 crystals. The actual frequency may not be that accurate but for amateur purposes, it doesn't matter that much. Go for it!
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KB1WSY
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« Reply #11 on: July 09, 2014, 05:25:55 PM »

Today was spent on various organizational tasks, but the main project was building a "chassis jig" to facilitate drilling holes in the chassis.

So here is Chapter Two, "Building a Chassis Jig" (for best results, click on the first photo, then click the "full screen" button at top left):

http://tinyurl.com/o8dt5v4

73 de Martin, KB2WSY
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K8AXW
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« Reply #12 on: July 09, 2014, 07:13:02 PM »

Martin:  Great idea about the "filler."  I've never seen this trick before. 
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K9MHZ
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« Reply #13 on: July 10, 2014, 03:55:33 AM »

building a "chassis jig" to facilitate drilling holes in the chassis.

So here is Chapter Two, "Building a Chassis Jig" (for best results, click on the first photo, then click the "full screen" button at top left):

73 de Martin, KB2WSY

Martin, the only thing that immediately stuck out was your use of a traditional drills instead of a Unibit.  Project cabinets are made from very soft and cheap aluminum, and will "gum up" traditional drill flutes.  Also, remember that a traditional drill will NOT produce a round hole....it will be a shape that's somewhat triangular distorted from true round. Unibits don't do that...you'll get a perfect hole. Especially with soft project cabinet aluminum, using a stepped Unibit is almost a necessity.  Keep your drill press speed down and use a drilling lubricant, even with a Unibit.

Also, because this aluminim is so soft, it will produce a sizeable burr on the inside of the cabinet.  Find yourself a deburring tool to run over a freshly drilled hole to get a nice cleaned-up hole.  Otherwise, your mounted hardware will not lay flat to the cabinet surface and you'll have poor results.

Good luck.

« Last Edit: July 10, 2014, 03:58:03 AM by K9MHZ » Logged
KB1WSY
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« Reply #14 on: July 10, 2014, 04:40:03 AM »

Martin, the only thing that immediately stuck out was your use of a traditional drills instead of a Unibit.

Indeed, I use high-quality Bosch bits specifically indicated for aluminum and so forth. I do own a couple of Unibits but have never used them.

Keep your drill press speed down and use a drilling lubricant.

I use the indicated speed for the material and size of hole, as provided by the drill press manufacturer. No problem so far. I always start with a small pilot hole and then progress to a larger bit if that's called for.

When drilling metal, I always lubricate the bit with "3-in-1" oil.

Also, because this aluminum is so soft, it will produce a sizeable burr on the inside of the cabinet.

I use a couple of old drill bits, larger than the drilled hole, and deburr by rotating the bits by hand. Seems to work fine and it's the technique suggested by ARRL in its manuals from 50 years ago.

However my key "anti-burr" technique is that the underneath of the aluminum is always clamped firmly against a flat piece of wood, with the clamp only an inch or two away from the area that's being drilled. This reduces the amount of burr, as well as preventing deformation of the metal. This is easy if you are drilling through a single piece of flat metal. For a prebuilt chassis such as the Bud in this case, it requires some kind of jig.

For large holes, I have a set of eight Greenlee punches.

Thank you for your post -- sometime I'll try out the Unibit!
« Last Edit: July 10, 2014, 04:44:35 AM by KB1WSY » Logged
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