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Author Topic: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build  (Read 201126 times)

G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #45 on: July 16, 2014, 11:30:54 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.

'Tis done. I'm on the road, but sneaked into a Lowes and spotted a likely heat gun model, which seemed pricey but has two speeds and variable heat. The main thing, for heat-shrinking, seems to be making sure that the temperature will go *low* enough -- about 125C. There were cheaper models but the minimum temperature was too high (although no doubt ideal for stripping paint!).

In the end I didn't buy the gun at Lowes, I bought it on Amazon with Amazon Prime and ended up paying about 35 percent less. It will probably arrive tomorrow, at home (I'm on the road): we have a regional Amazon distribution center quite close and with Prime, the two-day shipping usually ends up being one day.

I also bought, for $7 from Amazon, a large assortment of heat shrink tubing in 6" lengths.

You can never have too many tools.

73 de Martin, KB1WSY
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KK4MRN

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #46 on: July 16, 2014, 12:38:08 PM »

Quote
You can never have too many tools.

I agree.   My XYL may differ.

I have a heat gun that was bought for $5 from Harbour Freight Tools.  We have a few stores here in town.   Other stuff I've gotten from there: black plastic ties, digital multimeter, etc...

I recently bought a LCD frequency counter from an ebay seller.   Sure, I can use a general coverage receiver for verification, but I wanted to make it easier to know for sure.  Plus, this can come in handy for those radios that do not have a display.

One tool I want to get is a signal source.  Or maybe build one myself.    Maybe building a crystal oscillator for the signal I need would work...

Hopefully, you are not far from finishing your transmitter.

Recently, lost a nut for my MFJ key.  Consequently, it was a good excuse to get a better key...  I got a Nye oval key from Morse Express.

73 de Daniel, KK4MRN
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G3RZP

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #47 on: July 16, 2014, 03:01:24 PM »

>You can never have too many tools.<

Difference with KK4MRN is that my XYL agrees!
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K8AXW

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #48 on: July 16, 2014, 08:20:44 PM »

Martin:  No need to spend big bucks on a heat gun.  For one thing it isn't used THAT much. 

Most tools just take up valuable space, collect dust and seems like a waste of money.....until you need it!  Then it becomes the most valuable item in the house!!

The only time you can have too many tools is if you can't walk through the shop.
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #49 on: July 20, 2014, 02:49:28 AM »

I'm back home. During a visit yesterday to ARRL Labs in Newington, Connecticut I saw this in a glass display case. It's an original build of the 1968 "Novice Station" done more than 40 years ago!




Here's mine -- as you know, that transmitter is still under construction:


« Last Edit: July 20, 2014, 02:54:35 AM by KB1WSY »
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K8AXW

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #50 on: July 20, 2014, 09:03:36 AM »

Martin:  I notice your toggle switch goes up/down whereas the original goes left/right.   ::)

BTW, what receiver is that to the right?  In what magazine/Handbook was it published?
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #51 on: July 20, 2014, 10:58:01 AM »

BTW, what receiver is that to the right?  In what magazine/Handbook was it published?

See here: http://www.eham.net/ehamforum/smf/index.php/topic,90273.0.html.
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #52 on: July 20, 2014, 04:07:50 PM »

Today was a good day.

Here is Chapter Eight, "Finishing the Power Supply, Building the Oscillator and Part of the Power Amplifier":

http://tinyurl.com/m5eyjjq.
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K8AXW

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #53 on: July 20, 2014, 09:37:04 PM »

Martin:  Thank you for the link.  I recall following this post now.

Your work is exemplary!
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #54 on: July 21, 2014, 05:02:37 AM »

Here is Chapter Nine, "Building the Tank Output Circuit":

http://tinyurl.com/kf7nz9e

At this point the transmitter is essentially finished. I still need to check every connection against the circuit diagram, then test the TX, and troubleshoot if necessary.

However there is also an optional, two-transistor sidetone oscillator which should be very useful for a code novice such as myself. So I will be building that next, prior to testing the whole package.

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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #55 on: July 21, 2014, 08:13:55 AM »

Seeking some advice. Judging from some previous experimentation with the two-transistor sidetone circuit, it is likely that its output will be much too loud. I built pretty much the same circuit as a code practice oscillator last year and found that I had to insert a 68K resistor in series with the 9V supply battery in order to reduce the volume sufficiently, as heard in my high-impedance headphones.

According to the ARRL book, the sidetone oscillator is powered by the 5-volt to 7-volt voltage drop across 100-ohm resistor R4 when the transmitter is keyed. I'm thinking of putting a small 100K potentiometer between the negative terminal of M1 and the bottom end of resistor R10 (see schematic below). Presumably the sidetone oscillator presents a high input impedance (otherwise it would be draining dangerous amounts of power) hence the need for a relatively high-value pot, to make any difference to the volume. Another criterion: the "volume control" must work in such a way that it does not appreciably alter the audio frequency of the sidetone.

Do y'all think my plan (to add a 100K pot) is along the right tracks? Is there a better place in the circuit to control the volume?



73 de Martin, KB1WSY
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G3RZP

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #56 on: July 21, 2014, 11:20:35 AM »

Martin

Substitute a 10kohm pot for R12, and connect C17 to the wiper of the pot. Much more sanitary, although you will get some change infrequency as the pot is changed.

73

Peter G3RZP
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #57 on: July 21, 2014, 02:21:05 PM »

Martin

Substitute a 10kohm pot for R12, and connect C17 to the wiper of the pot. Much more sanitary, although you will get some change infrequency as the pot is changed.

73

Peter G3RZP

Thank you Peter. Meanwhile I have posted another couple of photos in Chapter Nine (tank circuit): just for fun, I checked the tank circuit with my trusty Eico 710 grid-dip meter and confirmed that rotating the Tune control results in resonance in the 40m band.
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G3EDM

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #58 on: July 23, 2014, 08:17:22 AM »

Here is Chapter 10, "Building the Sidetone Oscillator":

http://tinyurl.com/ol8ms5u

A reminder once again: the best view of the photos is when you open the first photo, then click on the "full screen" icon near the upper left.

The transmitter is now officially "finished" including the optional sidetone monitor.

Next: checking all of the wiring against the schematic, followed by a round of tests into a dummy load. I'm not doing this today because (1) I'd like to have a clear head and I'm rather tired after a 7-hour "final sprint" of building that began at 4:15 a.m., and (2) work pressures are such that it may be a little while -- a few days -- before I can find the time. We'll see.

Among other things, I think I spotted a couple of connections that were crimped, but never soldered. So it does need a careful going-over before powering up.

73 de Martin, KB1WSY




« Last Edit: July 23, 2014, 08:22:52 AM by KB1WSY »
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K8AXW

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RE: "A Simple Two-Tube Transmitter" ARRL 1968 -- Build
« Reply #59 on: July 23, 2014, 09:01:43 AM »

Martin:  What can I say, other than, "Absolutely beautiful job!"  Congratulations on not only the completion of a nice piece of gear but for the equally great job you did with the photos. 

This continuous post should be an inspiration to others to try their hand at building, which in my opinion is the greatest part of ham radio.

One thing for your consideration.  Rewire the side-tone osc. so the pot is reversed and the shaft can be accessed through a hole in the bottom plate.  But....... since this isn't your main rig, the hell with it!   ::)

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