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Author Topic: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build  (Read 201127 times)

K8AXW

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #15 on: July 10, 2014, 08:05:45 AM »

Martin:  As an avid builder for decades, it looks like you have your stuff together!!  Good thinking; good planning; proper equipment and understanding of it.  Way to go!
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KA0HCP

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #16 on: July 10, 2014, 08:53:30 AM »

Great tips, gang!
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G3RZP

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #17 on: July 10, 2014, 09:28:52 AM »

Martin,

You will want to use an external antenna tuner if you put it on the air in anger. Not because the pi network is not pretty wide range in impedance matching, but to make sure the harmonics are down to FCC levels.

I have a number of blocks of wood I use to support boxes etc for drilling and large hole cutting; with a suitable block and clamps, it's fine, but I'm much lazier than you!
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KB1GMX

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #18 on: July 10, 2014, 04:08:44 PM »

Unibits do the holes in that material well and very quickly.  For lube on Aluminum I use a plain
white plumbers candle rubbed on the cutting edge.  Those require far less pressure to cut well.

FYI: I used to drill the tops of those chassis from the inside while on a plank of wood.

The really cool way for the larger holes and odd shaped ones is a minimal set of drills
 and a Greenlee chassis punch set.

A note on those crystals (FT243) many of those may be "dead" or very inactive now.  The
usual reason for this is the gasket has contaminated the crystal blank.  They can be opened
and with care to not break or chip they can be cleaned.  That often restored full activity.

Also the usual trick for older transmitters was to put a #49 lamp in series with the crystal
to limit drive current.


Allison

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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #19 on: July 10, 2014, 04:53:35 PM »

A very productive day. I tackled one of my dreaded tasks: properly mounting the variable capacitor for the transmitter Tune control. From previous experience I know that this can be very tricky. With my receiver project, I had to make quite a lot of adjustments to the two variable capacitor mountings; the initial positioning was very slightly off, out of alignment, causing various problems.

Now that this is over, I can get on with the much easier task of drilling the holes for the other, less "positioning-critical" transmitter components.

Chapter Three, "Mounting a Variable Capacitor," is here: http://tinyurl.com/lc95zc5.
« Last Edit: July 10, 2014, 05:07:31 PM by KB1WSY »
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K8AXW

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #20 on: July 10, 2014, 08:36:34 PM »

Martin:  Beautiful and very accurate work on drilling the holes for the cap.  Have a question.... why not use just the two front cap mounting holes?  You eliminate 4 holes, 4 screws and 4 spacers as well as associated nuts and lockwashers.

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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #21 on: July 10, 2014, 10:17:21 PM »

Martin:  Beautiful and very accurate work on drilling the holes for the cap.  Have a question.... why not use just the two front cap mounting holes?  You eliminate 4 holes, 4 screws and 4 spacers as well as associated nuts and lockwashers.

I knew someone was going to ask that!

I originally hoped to do it that way, but this @?%! capacitor just isn't designed that way. When I tried mounting it with only the front screws, the capacitor tilted backwards: badly enough that the shaft and knob had a noticeable upward tilt. This is not noticeable in the photo of that stage because it's photographed from the front of the chassis, not the side. (I had anticipated a possible "tilt" problem beforehand, which is why I prepared those spacers and long screws in advance, since I was fairly sure I'd end up needing them.)

I initially thought the tilt was because the shaft hole was too small and that the tilt was caused by a raised area around the shaft front, but the problem persisted even after I enlarged the hole to clear the raised area. BTW the two front  mounting holes are not aligned horizontally with the shaft, but some distance below it (this is visible in the photo). This is probably also part of the problem. All of this happened about halfway through the sequence of photographs, but I did not document it.

Those old "receiver type" 365pF capacitors are tough to mount, with their U-shaped armatures, built-in threaded screw holes and small clearances for the screw ends. I suppose some of them originally came with a paper template for drilling the holes, although judging from the ARRL book, the issue of "figuring out where to drill the holes" was commonplace. The ARRL book devotes an entire page to the issue.

What I could have done is used only two screws/spacers under the top panel, not four, since I already had the two other screws on the front panel. But since I was "there" anyway I just went the whole hog and did all four. The "Tune" control on a transmitter probably doesn't need the sort of rigidity that would be called for in, say, a transmitter VFO capacitor or a receiver tuning control. But I thought I might as well "practice" mounting the capacitor "properly," since I know I'm going to be doing a lot of these in the future.
« Last Edit: July 10, 2014, 10:48:52 PM by KB1WSY »
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #22 on: July 11, 2014, 03:46:24 AM »

You will want to use an external antenna tuner if you put it on the air in anger. Not because the pi network is not pretty wide range in impedance matching, but to make sure the harmonics are down to FCC levels.

Dave, W7UUU, has built a variant of this transmitter design (which is often referred to as the W1TS transmitter) and uses it actively. Dave, are you having a problem with harmonics? Maybe you're already using an external antenna tuner or a low-pass filter?

I had not planned to use an external tuner unless the antenna situation becomes sub-optimal. I have preliminary permission from my landlord to erect a full-size, coax-fed 80m/40m trap dipole arranged as an inverted-V so the match with the pi network should be very good. If my landlord and/or his wife decide they don't like my antenna, I may have to opt for something more stealthy and may need a tuner. Thank you for the advice.

I have a number of blocks of wood I use to support boxes etc for drilling and large hole cutting; with a suitable block and clamps, it's fine, but I'm much lazier than you!

Peter: There are several forms of laziness. Mine takes the form of procrastination. This transmitter project has been on the blocks for 45 years. That's right, it's in 1969 that my parents gave me "How to Become a Radio Amateur" and a Heathkit code oscillator kit for my birthday. I got as far as building a home-made tin "chassis" in the school workshop, but never populated it with parts. More recently, I became licensed in the USA more than two years ago and bought all the parts for this transmitter more than a year ago! They've just been sitting on the shelf!

It's true that work and family pressures were the main reason I didn't get the time to start building earlier. But it's also a maddening character streak: I like to get everything "perfect" and plan obsessively in advance. Result: things take ages to get done.

Quote from:  link=topic=97719.msg769395#msg769395 date=1404922368
Martin, you should keep and cherish that box of FT crystals!

Al (K8AXW): I sure will. I'm 57 years old. Let's imagine I live to age 87. By then the crystals will be at least 90 years old!

FYI: I used to drill the tops of those chassis from the inside while on a plank of wood.

Allison: That's not always possible. There is a flange on the inside of the bottom of the chassis (for fixing the bottom plate) which gets in the way, even if you have a drill bit extender -- and I don't like extenders much, partly from a safety point of view. That places a limit on the location of the holes, because of the width of the chuck, among other things.

Thank you for the tip about using a plumbers' candle for lubrication.

The really cool way for the larger holes and odd shaped ones is a minimal set of drills and a Greenlee chassis punch set.

Good to have the endorsement, because that's exactly what I have. A set of conventional bit, and then eight Greenlee punches. These include the standard sizes for tube sockets etc. as well as some more exotic sizes, some of which are not made any more and had to be bought from an antique tool dealer. (Some components in these old ARRL books call for "intermediate" size holes that are no longer available in the Greenlee catalogue.)

A note on those crystals (FT243) many of those may be "dead" or very inactive now.  The usual reason for this is the gasket has contaminated the crystal blank.  They can be opened and with care to not break or chip they can be cleaned.  That often restored full activity.

That's very useful to know. Fortunately, these crystals have seen duty relatively recently. I purchased them from Paul, K7IN, who was downsizing his shack and getting rid of older equipment including the crystals and a mint-condition Eico 720 transmitter. (I didn't buy the TX because of my "all-homebrew" philosophy.) I got the impression he had been using the crystals in that TX until relatively recently. However if there are any problems, I will follow your advice about checking the gasket. Thank you.
« Last Edit: July 11, 2014, 03:52:58 AM by KB1WSY »
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G3RZP

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #23 on: July 11, 2014, 07:25:06 AM »

Martin,

Unless the harmonics have been measured with a spectrum analyser, you won't know if it's legal or not. The fact someone may or may not have had a problem isn't that much of a good guide. An antenna tuner will certainly help.....Or see if you hear from the Famous Candy Company.....but it's a bit late then...

One possibility is to use a half wave filter for each band - then the match is relatively unimportant.

Cleaning FT243 crystals. The usual trick was a wash in warm soapy water, followed by a rinse in clear water, followed by (in the old days!) a clean up in carbon tetrachloride. You can't get that now, but de-natured alcohol or acetone (nail varnish remover) should do. Handle them by the edges after the alcohol clean, and dry on tissues..
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K8AXW

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #24 on: July 11, 2014, 08:35:57 AM »

Martin:  This thread of your build is, to me, one of the most interesting things I've read here on eHam.  Perhaps your procrastination will be offset with these postings.  ;D

I've always mounted these variable caps by the two front screws and have on occasion created the third at the 12:00 o'clock position by drilling and tapping a new 4-40 screw hole.  However, you found you had a problem and solved it in a remarkable way.  I studied your method of "hole layout" and compliment you on it.

Once again, you're doing great work and the photos are equally remarkable.  I check this thread each day waiting for the next step.  Most interesting reading.

Oh, don't ever get put off by any comments or suggestions on "what you should have done" Martin.  This is just another version of "looking over one's shoulder" with the almost insatiable desire to grab it and doing yourself!   ;D

Al - K8AXW
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #25 on: July 11, 2014, 09:05:23 AM »

Unless the harmonics have been measured with a spectrum analyser, you won't know if it's legal or not. The fact someone may or may not have had a problem isn't that much of a good guide. An antenna tuner will certainly help.....Or see if you hear from the Famous Candy Company.....but it's a bit late then...

One possibility is to use a half wave filter for each band - then the match is relatively unimportant.

So what did Twelve-Year-Old Novice Builder do in 1969, lacking a spectrum analy(s/z)er? Or has the FCC become more stringent about harmonics? My general impression is if anything there is less of an issue because (a) TVI is less  of a problem now that TV Band I and III have been largely vacated of TV, and (2) the FCC seems to have fewer enforcement resources than in the days of yore (not that this is any excuse to break the rules).

I like the idea of a halfwave filter. I've always been intrigued by this one, which is two halfwave filters (40m and 80m) mounted inside a coffee can. It comes from "Understanding Amateur Radio," 1963 edition. I have a whole pile of those miniductors that I could use for this:



Quote from:  link=topic=97719.msg769853#msg769853 date=1405092957
I've always mounted these variable caps by the two front screws and have on occasion created the third at the 12:00 o'clock position by drilling and tapping a new 4-40 screw hole.  However, you found you had a problem and solved it in a remarkable way.  I studied your method of "hole layout" and compliment you on it.

Al (K8AXW): Thanks for the compliments. I don't have thread taps in my workshop and it's a good 40 years since the last time I tapped a thread! There were also some additional holes in the front of that capacitor, but they weren't tapped, so I would have had to insert a nut between the plates and the armature. But the nut would probably have been too thick and would have caught on the plates. BTW all the screws are #6.

Quote from:  link=topic=97719.msg769853#msg769853 date=1405092957
Oh, don't ever get put off by any comments or suggestions on "what you should have done" Martin.  This is just another version of "looking over one's shoulder" with the almost insatiable desire to grab it and doing yourself!   ;D

Don't worry, I won't be put off. Nearly all of the comments include useful information and tips to do things better. Furthermore, everyone knows I'm a relative beginner and they won't know what I already know, and what I don't already know. (Yeech, I'm sounding like Donald Rumsfeld.)
« Last Edit: July 11, 2014, 09:14:40 AM by KB1WSY »
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G3RZP

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #26 on: July 11, 2014, 02:31:55 PM »

Martin,

Specs have become much tighter since 1969. Especially after the 1993 WARC, where the radio astronomers were complaining about spurious emission from Iridium satellites. This led to the setting up of  ITU-R TG1/3 which for the first time proposed limits for amateur stations, which were incorporated (by   a very complex route into the Radio Regulations in 1996) as a result of ITU-R Task Group 1/3. The FCC regulations require harmonics and spurs to be -43dBc for transmitters below 30MHz. The ITU requires in the International Radio Regulations (ITU-R SM329) that amateur transmitters operating below 30 MHz have all harmonics and spurious emissions suppressed by 43 + 10 log P dB without having to be more than 50dB down. The FCC screwed up (big surprise!) by forgetting the 10 Log P - in spite of the fact that the FCC delegate to the ITU meeting is a Ham, and the FCC guy who wrote the rule is a ham!

All of this was resulted in me ending up at ITU defending amateur radio interests at ITU Study Group 1 for the next 16 years.....as well at the CEPT Study Group Spectrum Engineering.............
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #27 on: July 11, 2014, 05:59:16 PM »

Hellos guys and gals. Today was a serious "metalwork" day. I am using the detailed drilling templates from the original ARRL book, but some of my components have a different form factor. Therefore the templates have to be adapted.

Chapter Four, "More metalwork," is here: http://tinyurl.com/p9z67hw.
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KC2ZFA

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #28 on: July 12, 2014, 08:57:44 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.
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KA0HCP

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #29 on: July 12, 2014, 09:24:28 AM »

Hams should always make good faith efforts to have the cleanest signal practicable.  However, the FCC has never mandated the retiring, or major modification of older transmitters to meet newer standards.
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