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Author Topic: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build  (Read 201129 times)

G3RZP

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #30 on: July 12, 2014, 09:28:12 AM »

Martin,

Some years back, I got a set of US taps and dies in several sizes from 4-40 to 1/2 inch from Sears, and the price was reasonable - around $40 then for quite a number. Worth looking at.

KB4QAA,

The International Radio Regulations required the new spurious levels to be met for new equipment from Jan 1, 2003 and for ALL equipment from Jan 1, 2012.  The FCC may yet get around to questioning things if there's a problem, and anyway, this IS a new equipment, not an old one!
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #31 on: July 12, 2014, 11:37:57 AM »

great work.

the bulk of the ceramic xtal socket shold be below chassis, with only the raised part (where the xtal legs plug in) protruding through the chassis.

Thanks. I am aware of that, but for some reason some of the ARRL projects from this era showed the sockets mounted above chassis. Call me strange, but I'm actually trying to make the TX look as close to the original design as possible, even down to odd details like that one. (And of course, the XTAL socket will work alright, either way.)

Other strange things I am doing: using exactly the same sockets even though they would be considered non-standard nowadays. So, for instance, the telegraph key socket is a phono socket (not a 1/4" jack socket); and the antenna is also a phono (not a UHF connector). The high-impedance headphones plug into the sidetone oscillator using those ancient connectors called "tip jacks."

I am making only two exceptions to the rule of "historical accuracy":

(1) If my components aren't the same form factor as the original ones, I am making slight adjustments to the positioning, such as when I moved V1 slightly to the right in order to avoid the tube being too close to the power transformer.

(2) Safety. I am using a three-wire AC cord and putting an IEC receptacle on the back panel along with a chassis-mounted fuse on the Live side of the circuit, and grounding the chassis to mains ground. (The original design has two-wire "lamp cord" and a double-fuse system because the plug was unpolarized.) Historical accuracy is all very good, but it's trumped by Stayin' Alive!

This transmitter, and its companion receiver that I built last year, are basically a "one-off" exercise designed to replicate the station that I wanted to build as a 12-year-old, but never did. Once I've got that out of my system, my designs will become more personal and not hew strictly to ARRL designs!

73 de Martin, KB1WSY

« Last Edit: July 12, 2014, 11:45:04 AM by KB1WSY »
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #32 on: July 12, 2014, 05:33:38 PM »

A very good day.

Chapter Four: Finishing the Metalwork

Click here: http://tinyurl.com/pnxhhuq

A reminder: Once you've clicked on the link, the best way to go through the pictures is to click on the first photo, then click on the "full screen" option near the upper left of the screen and then use the right-arrow key on your keyboard to cycle through the photos.
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K8AXW

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #33 on: July 13, 2014, 09:37:25 AM »

Quote
he bulk of the ceramic xtal socket shold be below chassis, with only the raised part (where the xtal legs plug in) protruding through the chassis.

As a rule, correct.  However, I've seen them mounted BOTH ways.  

Martin, Peter mentioned the tap sets.  They're great to have along with the T-handle chuck to use with them.  Just something to put on your "acquire list."

Another thing for your acquire list are the spring loaded center punches.  One light/small punch for aluminum jobs like your're presently doing and the larger one for making dimples in steel.

« Last Edit: July 13, 2014, 10:22:31 AM by K8AXW »
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #34 on: July 13, 2014, 04:24:10 PM »

Here's a rather short Chapter Six, "Assembly Begins":

http://tinyurl.com/p868gvc

By the way I've just realized that my post yesterday provided a link to "Chapter Four: Finishing the Metalwork" but actually that should have read, "Chapter Five." Sorry about the mixup.

73 de Martin, KB1WSY
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #35 on: July 14, 2014, 02:40:21 AM »

Hello gang:

Quick question. My Hammond power transformer includes a lead for the transformer's electrostatic shield. A quick search on the Internet was rather confusing, and the Hammond website seems to be silent on the matter.

To me it seems logical to connect that electrostatic shield to ground. Which is what I will do unless someone suggests otherwise.

(I am not sure why the shield wasn't just internally connected to the transformer's armature/casing, which after all will be grounded as it is screwed to the chassis. But I suppose there might be applications in which the transformer case would be isolated from ground.)

73 de Martin, KB1WSY
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #36 on: July 14, 2014, 07:11:52 AM »

Quick question. My Hammond power transformer includes a lead for the transformer's electrostatic shield....

Actually never mind. The specification sheet that came with the transformer said there was a gray lead for the electrostatic shield, but looking at the actual transformer, there is no such lead (and all the other leads check out, in terms of color coding, with the spec sheet). So apparently just a documentation error.

73 de Martin, KB1WSY
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K8AXW

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #37 on: July 14, 2014, 09:10:05 AM »

Just for the record Martin, the electrostatic shield lead, which is usually bare braid, is indeed grounded close to the transformer..... like to one of the mounting screws.  If that proves difficult then add a ground lug close to the transformer mounting screw.
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #38 on: July 14, 2014, 10:27:19 AM »

Work today was slow, but good.

Here's Chapter 7, "Building the Power Supply":

http://tinyurl.com/m5wzxq3

I will be traveling for the next week -- including going to the ARRL Centennial Convention in the second half of the week. So, this transmitter project will now take a break for about one week.

73 de Martin, KB1WSY
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #39 on: July 15, 2014, 09:05:22 AM »

While building the power supply, I bundled the wires of the transformer's primary together with little plastic ties and also insulating tape (which I used, in part, to condemn the loose ends of the two 100V wires that I will never use).

I've now decided this method was too ad-hoc (and its ugliness bothers me) and I'm also slightly worried about the longevity of the insulating tape. So in a fit of perfectionism I've decided to replace this "sheath" with heat-shrink tubing, which will be much neater and presumably lasts more or less forever.

I don't own the tools for this. Am I right that what I need is a kit of tubing in various sizes, and a heat-shrink "gun" which blows hot air? (That's what I found on the Internet.) Sounds like the perfect kind of tool for these situations. I haven't soldered those wires down yet so it would be easy to unwrap the insulating tape and substitute the heatshrink.

How do you decide what size of tube to use? I read somewhere that the tube should be about twice the diameter of the bundle of wires, i.e. that it shrinks to half its diameter when heated.

73 de Martin, KB1WSY
« Last Edit: July 15, 2014, 09:07:55 AM by KB1WSY »
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N7EKU

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #40 on: July 15, 2014, 03:04:54 PM »

Hi Martin,

For heatshrink, you can just use a butane lighter.  We used heatguns at work, but using lighters on heatshrink at home works just as well for me.

For sizing, you can always test shrink a small piece -- they usually seem to shrink to about half original diameter.  I usually just pick a size that loosely fits over what I want to heatshrink.  Of course if you go thicker, then the heatshrink layer will be thicker.

If what you are shrinking on to is very smooth and slick, heatshrink can slide out of place.  You can put silicone sealant inside before shrinking, for good adhesion and waterproofing.

A couple of other points...

Others have mentioned using an antenna tuner for reducing harmonics.  This is not a sure-fire way to do it as, depending on the type of tuner and how you have it set, they can be highpass which is not much help!

Since it sounds like you are moving on the high voltage, Martin please be very careful.  Besides all the other cautions about working around HV, keeping one hand in your back pocket at all times when making measurements, or shorting capacitors, is a rule to LIVE by!

73,


Mark/n7eku



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Mark -- N7EKU/VE3

K8AXW

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #41 on: July 15, 2014, 08:29:06 PM »

Martin:  My suggestion is to place an order with Jameco Electronics (Jameco.com) and order 4ft lenghts of heatshrink tubing of various sizes.  (Black) When you get it cut it up into about 10" lengths and put all of it in a suitable box. 

This stuff comes in handy quite a bit when building electronic gear.  For example, aside from the use your going to use it for, I also use small pieces at the end of some wires that are subject to a lot of flexing.  Like probes and the like.  The heatshrink tubing acts like a strain relief.

I also suggest you spring for a heat gun.  I've used everything from matches to butane lighters.  The matches cover the tubing with soot and it's necessary to be extremely careful that you don't burn the tubing with the butane lighter.  It works but not as good as a gun.

Like shrink tubing, the heat gun will come in handy for other things.  Get one with a High and Low temp setting and if it has a setting with no heat so much the better. Heat guns make a nice even shrink since you heat all around the tubing, not just one spot.

If it doesn't have the "no heat" option don't pass up an opportunity to grab a hair dryer with the "no heat" switch position.  Hair dryers are great for cooling joints.

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N7EKU

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #42 on: July 15, 2014, 10:01:21 PM »

Extremely careful?

Not true in my experience at all.  I find heatshrink to be quite tough.  I'm not all that careful with it and I've used a little Bic type lighter to shrink at least five or six dozen pieces at home -- haven't burned a single piece yet.  The flame naturally wraps around the shrink and you just twirl it if the wire is free to spin, or come at it from different sides if not, and it shrinks very well.

I feel you actually need to be more careful with a heatgun than with a lighter.  Heat guns pack way more power than a lighter so if you get too close or leave them too long they'll burn paint or insulation, or melt other stuff.  If you get one, definitely use it on the low setting for heatshrink.  On high you can use them to melt solder!  (Don't try either setting to dry your cat.)

73,


Mark.








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Mark -- N7EKU/VE3

G3RZP

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #43 on: July 16, 2014, 03:27:01 AM »

Shrinking heatshrink is another great application for a cheap hot air gun. I use a dual speed gun, intended for paint stripping. Try Sears, Home Depot or any of your local DIY shops. It's good too for stripping parts off PC boards, and soldering PL259s and the like.
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K8AXW

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #44 on: July 16, 2014, 09:30:29 AM »

Quote
(Don't try either setting to dry your cat.)

Nor do you want to hand your wife a cocked .45 Colt to dry her hair!
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