WT40: POPULATING the AUDIO AMPLIFIER CIRCUIT BOARD


[[ Most recent Update to this page – 27 October 2012. ]]

THIS BLOG ENTRY CONTAINS:

[] Introduction (You are here.)

[] Audio Amplifier Module Parts List

[] Preparing the 2N3053 Transistor

[] Preparing the Circuit Board

[] Tie Points

[] Jumpers

[] Initial Check-Out

Building of the WT40 Transceiver will begin with the Audio Amplifier module and proceed “backward” through the modules until we get to the antenna connection.


For just about everything you do in electronics there are at least two ways to do it; sometimes there are dozens of ways to accomplish the same thing. This means choices must be made. For the purpose at hand, I have made some of those choices for you. I have chosen to use discrete components for the Audio Amplifier because I think discrete components are easier to work with.

Begin the building process by collecting all the parts.

WT40 AUDIO AMPLIFIER MODULE PARTS LIST

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Resistors
1/4 Watt, plus or minus 5% tolerance.
Values shown in Ohms; k = x 1000.

[] One: 10
[] One; 150
[] One: 220
[] One: 1k
[] One: 2.2k
[] One: 4.7k
[] One: 10k
[] One: 22k
[] Two: 47k

Quarter Watt resistors can be purchased for a penny each, or less, from parts suppliers such as JAMECO and MOUSER, – BUT – to get such a good price, they must be purchased in lots of 100, or more pieces. For small projects, such as the WT40 Transceiver, it is probably less expensive to pay the “extra” few cents to purchase them in smaller quantities.

Alert readers, such as yourself, will have noticed that the 47k resistor on the far right in the photo is physically larger that the others. That’s because I didn’t happen to have a 47k quarter watt resistor on hand at the time I was taking the picture, so I substituted a half watt. The physical size has nothing to do with the resistance value.

Experienced builders will probably have noticed that the resistors in the photo line up, left-to-right, according to value, 10 Ohms on the left, and progressing to the 47k resistor on the right.

Audio Gain Control
Plus or minus 20% tolerance, 1/4 Watt, Audio Taper Potentiometer (logarithmic).

[] One: 10k, JAMECO # 255426, or equivalent.

NOTE: The Audio Gain potentiometer mounts on the Control Panel, NOT on the circuit board, but you might as well add it to your parts collection now because you will need it during check-out of the Audio Module.

You may be wondering . . . What about a knob for the potentiometer? That’s a good question. Actually, no knob is needed at this point in the game because the shaft is easily turned without a knob. Knobs and switches will be detailed when we get to the Front Panel, much later in this series. You can, of course, get a knob now – just be sure it will fit the shaft on the potentiometer you choose for Audio Gain control (the shafts come in different diameters, and some are slotted or half-moon shaped).

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Capacitors
Plus or minus 20% tolerance, Monolithic Ceramic, Type Z5U, or equivalent.

[] Three: 0.1 uF

Polarized Electrolytic Capacitors

Plus or minus 20% tolerance, Radial -Lead, rated for 16 volts or more.

[] Three: 10uF
[] One: 47 uF
[] One: 220 uF

NOTE: Electrolytic capacitors of a given capacitive and voltage rating come in different physical sizes. I suggest you obtain the smallest size available from your parts supplier (Excluding surface – mount capacitors, which is story for another day).

Miscellaneous Parts

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[] One: Radio Shack #276-148 Dual Circuit Board, or equivalent .

[] Mounting Hardware for the circuit board. The exact hardware for mounting the modules will depend upon how the builder (YOU) decide to package your transceiver. At this point in the building process, the main purpose for the standoffs is to provide an Anchor at each corner of the circuit board for the Ground Buss. The standoffs listed here can be useful during final assembly of the transceiver, no matter what packaging procedure is used.

[] Four: 1/4 inch, Hex 6-32 threaded, male/Female standoff, 1/4 inch long, JAMECO #133542, or equivalent.
[] Four: 3/4 inch, Hex 6-32 threaded, Female/Female standoff, 5/8 inch long JAMECO #77623, or equivalent.

[] One: Heat Sink for the 2N3053 transistor, MOUSER part number 532-323005800, or equivalent.

The heat sink fits snuggly on the transistor, and will require quite a bit of pressure to mount it. Take care not to damage either the heat sink or the transistor when mounting the heat sink.

The transistor and heat sink should look something like the photo, below, after mounting the heat sink.

Notice that the legs of the transistor have been formed for inserting onto the circuit board before the heat sink was mounted.

Most any heat sink for a TO39 transistor will do the trick. “TO39” simply means “Transistor Outline number 39”, referring to a line drawing that shows the outline of the transistor. The 2N3904 transistor used for the preamplifier is a TO92, and needs NO heat sink.

You can fabricate a heat sink adequate for this application using #20 or #22 bare copper wire, as shown in the photo, below.

A wire heat sink requires the transistor to have a metal case so the heat sink can be soldered to the case.

Making a heat sink this way uses about six inches of wire, and is a rather labor intensive task, which requires a bit of practice to get the wire shaped “just right”, so it is not a job to be taken lightly.

Back to the parts list . . .

[] About 19 inches: #22 bare copper wire for the Ground Buss and Tie Points. (And another six inches, or so, if you plan to make your own heat sink.)

NOTE: You will use about 12 feet of #22 bare copper wire for Ground Buss and Tie Points if you build all the modules in this transceiver following the procedure outlined here.

[] About 6 inches: #24 or #26 Stranded Hook-Up Wire for Jumpers.

Speaking of Jumpers, if you don’t already have them, it would be a good idea to get set of test / jumper cables with clips on each end, Radio Shack # 278-1156, or equivalent. these can be very useful during testing modules.

[] About a foot, or so, of 3-wire hook up cable (sometimes called “intercom cable”) to connect the Audio Gain potentiometer to the Audio Amplifier module during testing. I use salvaged, multi-color ribbon cable for this sort of thing because wire of any kind is usually sold by the pound and/or in spools of 100 ft or more, which is a lot of wire, and it would take a couple of lifetimes to use up a 100 ft spool of of #24 or #26 hook-up wire (unless you plan to do an awful lot of wiring). You may be able to buy wire by the foot at your local electronic parts outlet, and some Radio Shack stores still stock wire to sell by the foot – – ask for the 3-conductor intercom wire, #278-871.

This intercom wire cable may (or may not) be available at your friendly, neighborhood Radio shack store. There are several Radio Shack stores in the area where I live, and I have found that some stores carry a larger variety of items than others.

NOTE: 3-wire intercom cable, or equivalent, will also be need for testing of the Product Detector and VFO modules. This cable comes in handy for all sorts of things at the workbench, so you might as well stock a few “extra” feet for future use. “Equivalent” cable can be easily fabricated using three different colors of insulated hook-up wire twisted together.

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An assembled and tested Audio Amplifier module shown in the photo, below.

The red jumper wires on the circuit board are for distributing 12 volts to power various parts of the board. 12 volt power enters the circuit board at TP30, near the upper right-hand corner of the board in this photo.

The blue wire is a jumper to carry the signal from the Collector of the 2N3904 preamplifier Base of the 2N3053 Amplifier transistor.

Experienced builders may what to use a different layout, such as the one shown below, so that multiple modules can be placed on a single dual circuit board, RS #276-148, or equivalent.

This compact layout is electronically identical to the one shown earlier, and leaves half the board to be used for another module, perhaps the Product Detector and/or the Audio Buffer.

PREPARING THE 2N3053 TRANSISTOR

The “legs” on the 2N3053 transistor are pre-formed before the heat sink is mounted, as shown in the photos, below.

Notice in the photo that the collector leg is attached to the case. This means that there will be 12 volts present on the case whenever power is applied to the circuit board, and neither the case nor the heat sink can be touching any other component.

In the photo, below, notice that the 2N3053 stands about 3/16 of an inch above the surface of the circuit board.

Resistors and capacitors mount snugglyt against the circuit board.

More about this when we start POPULATING the circuit board.

A simplified diagram of the Audio Amplifier module is shown below.

This is a generic module with Power, Input Signal (from the Product Detector module), Output Signal (to Headphones and/or an OPTIONAL Speaker), and, of course, a GROUND connection – the connection that all modules must have.

The Audio Amplifier is more than adequate for headphone use, but is not suitable for direct connection to a speaker.  Yes, it will drive a small speaker directly, but the performance will be marginal, at best. A separate, amplified speaker unit, such as the ones pictured below, is recommended if you want room-filling sound.

The SONY speaker shown in the photo, was once part of a computer audio system. Similar units can sometimes be purchased in “thrift” stores for a couple of bucks (that’s where I got this one).

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This Sony unit measures about 6 3/4 inches tall by 2 3/4 inches wide by 4 3/4 inches deep. The unit is powered by either four “c” cells, or a 6 VDC “wall wart”. This is a nice little speaker unit, and I have used it several years, both on my workbench and as part of my Ham radio station.

Or – – you can build such a device to drive an external speaker, such as the one in the photo below. (More about this when we get to Optional Features.)

The home-brew amplified speaker shown was build (almost) entirely from junk box parts. For scale, the speaker is about 2 1/2 inches in diameter, and was salvaged from a discarded CB radio that I purchased at a thrift store. I purchased the “box to put it in” at the same thrift store for $ 0.25. Yep, for a quarter, I got a fine little box to house an auxiliary amplified speaker.

( “Thrift” stores are one of my favorite sources for parts ! )

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Be that as it may, I used this junk box speaker unit with an earlier version of the transceiver. This home-brew amplified speaker is now retired, and sits on a shelf along with other “retired” equipment I have built.

PREPARING THE CIRCUIT BOARD

As mentioned briefly in previous posts, once all the required parts are on hand, the next task is to prepare the 276-148 circuit board. The procedure shown here assumes that the Radio Shack #276-148 Dual Printed Circuit Board, or equivalent, is being used as the platform on which the modules will be built.

Notice the orientation of the circuit board – – the half on the left end contains 213 perforations for mounting components; the half on the right end contains 228 perforations. This is the orientation shown in the layout drawings and photos of the Audio Amplifier board.

FIRST, Mount Standoffs at each corner of the Radio Shack #276-148 Dual Circuit Board, or equivalent.

At this point in the process the standoffs will be serving as anchors at each corner for mounting the Ground Buss, which you can see looping around the standoffs in the photo, above. The recommended standoffs are:

[] 1/4 inch long Hex 6-32 Threaded Male / Female standoffs, JAMECO #133542, or equivalent, on the Solder Side of the circuit board.

[] 3/4 inch long Hex 6-32 Threaded Female / Female standoffs, JAMECO #77552, or equivalent, on the Component Side of the circuit board.

Much later in the building process, when the circuit boards are mounted in their final configuration, the standoffs can be easily removed and replaced with different length standoffs, if required to accommodate the needs of the configuration.

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ADD THE GROUND BUSS

When the standoffs are in place, ADD THE GROUND BUSS, using about 11 1/2 inches of #22 bare copper wire.
As you can see in the photo, the Ground buss loops around the entire circuit board.

At each corner, the Ground Buss passes through a perforation, goes around the standoff, then passes through another perforation back to the solder side of the board, then continues around the entire board in a similar manner.

Where the two ends of the Ground Buss meet, there should be about 3/8 inch overlap where the two ends are soldered together.

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TIE POINTS

Each circuit board will have several TIE POINTS. These are labeled TPx in the layout drawing, shone below. The number “x” is for identification. The points are added, as needed, as you mount components onto the circuit board.

Tie points serve three functions:

[] Connecting points between modules

[] Test points for module check-out
[] Terminus for jumpers within a circuit board. TPs for jumpers are, sometimes, simply a perforation in the circuit board through which a wire is passed and soldered to a component.

Tie points are shown on Layout Drawing in two forms:

[1] Bold black lines between two adjacent perforations . . .

[2] Gray circles around a single perforation . . .


The gray circles simply show where to insert one end of a Jumper Wire through a perforation.

The bold black lines between two adjacent perforations in the Layout Drawing represent a loop of #22 bare copper wire that has been fashioned into a Tie Point, as illustrated below.

A wire loop type Tie Point requires about 2 inches of #22 bare copper wire folding it into a “u” shape so it can be inserted into two adjacent perforations.

Twist the wire on both the component side and the solder side, as illustrated in the drawing, above.

NOTE: It is important that the bare copper wire if free of corrosion so that the solder adheres tightly to the wire. If there is any discoloration to the wire, clean it with very fine sandpaper, steel wool, or other fine-grained abrasive material.

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Form the wire to make a “U”. I find it best to form the “U” before cutting the Tie Point from the end of the wire.
Cut the wire to get a long, skinny, upside-down “U”.

The photo, below, shows a newly formed “U” that has been inserted into the circuit board to become a Tie Point for connecting to Ground, such as TP39 on the Audio Amplifier module. Tie Points that are Ground Connections, such as TP39, are placed in the perforations nearest to an edge of the circuit board.

The photo, below, shows the twists on both surfaces of the circuit board. These twists hold the tie point firmly in place.

There will be a bit is “excess’ wire on the solder side of the circuit board. Since this particular Tie Point is for a Ground connection, form about 1/4 inch of the two “legs” along the ground buss before soldering.

NOTE: If the Tie Point is NOT going to be soldered to the Ground Buss, it is best to leave the excess wire in place until after all the components being connected to the Tie Point are connected and soldered, then trim the excess.

The photo below shows a Ground Tie Point soldered to the ground buss.

Allow about 30 seconds, or so, for  the solder to cool, then solder the Tie Point on the component side of the circuit board.

Notice in the photo, below, that the loop portion of the Tie Point is covered with solder.

Tie Points that are NOT connected to ground, such as TP38, are placed so there is one or more perforations between them and the ground buss.

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JUMPERS

Jumpers, shown clearly on the Schematic, are omitted from the Layout Drawings because they tend to clutter the drawings.

Wire Jumpers are used to distribute signal and/or power to various parts of the circuit board.

INSTALL JUMPERS LAST, immediately before Resistance Measurements, as will be explained later, when we get to doing testing the circuit board.
INSTALLING  COMPONENTS  on  the  CIRCUIT  BOARD

Notice, on the Layout Drawing, that the OUTPUT SIGNAL tie point (TP38) is located TWO perforations away from the Ground Buss.

The GROUND tie point (TP39) is placed in the last perforation on the board and soldered directly to the Ground Buss.

The order in which the components (other than jumpers) are placed on the circuit board is a matter of personal preference. I started by placing the 2N3053 and its attached Heat Sink onto the circuit board, then added the other components and tie points.

Another approach which I have used successfully is to start by fabricating all the wire Tie Points, then adding the other components; transistors, resistors, capacitors, etc. The point being, use whatever approach to populating the circuit board that makes sense to YOU.

– – BUT – –

* * * * INSTALL JUMPERS LAST, as explained in detail, later. * * * *
PREPARING THE 2N3053 TRANSISTOR

The 2N3053 is an NPN Bipolar transistor housed in a TO39 metal case with three “legs” that allow connection to the Emitter, Base, and Collector; left to right in the photo, below.

Notice in the photo, below, that the Collector leg is connected directly to the CASE housing the transistor.


This is IMPORTANT because it means that voltage is present on the case when voltage is applied to the circuit, and the case and the heat sink must not touch any other component on the board.

Form the legs so that the 2N3053 will stand about 3/16 inch above the circuit board, as shown in the photo, below.

After the legs are formed properly, attach the Heat Sink before inserting the transistor into the circuit board.

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The Layout Drawing, below, shows the position of the perforation where the Emitter leg of Q6 is inserted through the circuit board.

The leg from the Emitter is inserted into the perforation 8 perforations from the right end of the board and 7 perforations up from the bottom.

Shown below is a top view of Q6,the 2N3053 transistor, mounted on the circuit board – – with the Heat Sink Removed – – to indicate where the legs pass through to the Solder Side of the circuit board, where the Base leg is soldered to the jumper wire coming from the Collector of Q5, the 2N3904 transistor. This solder joint is designated TP34 on the Schematic and Layout Drawings.


This photo was taken after one end of Jumper 6 (the blue wire) had been soldered in place at TP34.

It is important that JUMPERS be INSTALLED LAST, as will be explained in detail, later.
Components can be added to the circuit board in any order you wish. I recommend installing and soldering C36 from the Emitter of Q6 to TP38 next in order to hold Q6 firmly in place.

Be sure to orient C36 with the POSITIVE side connected to the Emitter of Q6.

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NOTE: Not all electrolytic capacitors are polarized, but the ones use in the Audio Amplifier module ARE POLARIZED. It seems a bit strange that the positive connection of a polarized capacitor is indicated on schematic drawings while the negative connection is indicated on the body of the capacitor. – – Just one of the strange little quirks of “standardized” notation used in electronics.
On the Solder Side of the circuit board, pictured below, the leads from components are formed firmly against the board with about 3/16 inch overlap, excess wire trimmed, then soldered.

The other connection to Q6 that will help hold it in place is C35, the 47 uF electrolytic capacitor that goes from the Collector to the Ground Buss, with the positive side of the capacitor to the Collector.

NOTICE, in the layout drawing, that the wire from the Negative side of C35 will pass under the 22k resistor R24 on the Solder Side of the board on its way to the Ground Buss.

Proceed to populate the remainder of the circuit board however you wish. Take your time and double check all connections before applying solder. Correcting wiring errors is sometimes necessary, but it is not much fun.

The photo, below, shows tha Solder Side of the completed Audio Amplifier circuit board.

NOW it is time to connect the JUMPER wires — BUT — solder ONLY ONE END, as shown in the photo, below.

Why connect only one end? (You might want to know.) Because we have not yet done Current, Resistance, and Voltage Measurements, which will be done in WT40 Audio Tests and Measurements.

The “loose” end of the jumpers will be used as Test Points for Tests and Measurements, then soldered in place when testing is completed.

Use insulated hookup wire for the jumpers. The color is arbitrary, but I always use red wire to carry 12 volt power, and some other color for signal connections.

If you are following the layout I have used, Jumper 4 from TP30 to TP37 is about 3 1/2 inches; Jumper 5 from TP31 to TP32 is about 2 inches; and Jumper 6 from TP33 to TP34 is about 1 3/4 inch. The lengths are not critical, but must reach from one point to another with little or no excess.

NOTE: If you are using stranded hook-up wire (which I recommend), about 1/4 inch of insulation mustt be stripped from each end and covered with solder BEFORE placing them on the circuit board. Twist the stranded wire tightly together on each end of the jumpers before applying older.

After all components have been soldered in place, it is time take a break and relax for a while in preparation for . . .

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INITIAL CHECK-OUT

First, a Few Words Regarding Testing:

Each module will be tested to make sure it is functioning properly before being connected to other modules for operational testing.

A generic test procedure is outlined below.

[] Visual Check to make sure all the components are present and properly soldered into place.

[] Resistance Check will reveal “short” circuits and “open” circuits.

[] Current Check to be sure excessive current is not being drawn, or that no current is being drawn in a circuit that should be drawing current.

[] DC Voltage Check to be sure the proper voltages are present at key points in the circuit.

[] AC voltage checking for signal processing modules.

( Of course, a passive module, such as the receiver 40 meter Filter, does not require testing for current and voltage. )

[] Operational check to verify the module if functioning properly.
The most likely cause of problems on a newly built circuit is a WIRING ERROR of one kind or another.

WIRING ERRORS include:
[] Missing components
[] Components not connected
[] Components connected to the wrong place
[] Connections not soldered
[] “Cold” solder connections
– insulation material, such as enamel, not removed before soldering
– not enough heat applied to flow the solder
– mechanical shock or movement before the solder solidifies
[] Solder “bridges” causing a “short” circuit between solder joints.

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VISUAL INSPECTION

Begin your check-out with a thorough VISUAL INSPECTION to make sure that there are no missing parts, and that everything is connected correctly and properly soldered. Defects will, of course, become obvious during resistance, current and/or voltage checks, but a good visual check can often spot errors that can be quickly and easily corrected before electronic testing begins and, thus, save a lot of time.

Begin your Visual Inspection with a COMPONENT COUNT.

[] On the Component Side of the circuit board, you should find:

[] Three Jumper Wires CONNECTED AT ONLY ONE END. (The unconnected end of the jumpers will be used as test points during Resistance Measurements and during Current Measurements.
[] Two Transistors, a 2N3904 and a 2N3053. The 2N3053 should have a heat sink attached.
[] Ten 1/4 Watt resistors.
[] Three 0.1 ceramic capacitors.
[] One 1N4148 diode.
[] Three 10 uF electrolytic capacitors.
[] One 47 uF electrolytic capacitor.
[] One 220 uF electrolytic capacitor.

If you find a discrepancy in component count, use the layout diagram and/or the schematic to find the error.

[] On the Solder Side of the circuit board, check to see that all components are correctly connected and properly soldered. I use a magnifying glass for this check because I have found that magnification sometimes shows problems that I would miss with the naked eye. Finding a wiring error or a bad solder joint with a visual check is a heck of a lot easier than tracking it down during resistance, current, or voltage checks.

Correct any errors found during the visual inspection before proceeding to WT40 AUDIO TESTS and MEASUREMENTS.

– END of WT40 POPULATING the CIRCUIT BOARD –

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About w6bky

Retired 29 May 1987. Now do hobbies: blogging, ham radio, gardening, etc.
This entry was posted in qrp, wt40 transceiver and tagged , , , , , , , , . Bookmark the permalink.

5 Responses to WT40: POPULATING the AUDIO AMPLIFIER CIRCUIT BOARD

  1. deltafour1212 says:

    I have a Technician License so how could I build this transceiver to where it only operates from 7.025-7.125 MHz?

    • w6bky says:

      deltafour,

      Excellent question.

      The short answer is that you can build the WT40 to operate anywhere in the 40 meter band and details are included in the VFO section of the building process.

      You have probably noticed that there has not been any blog entries beyond the introduction to the receiver portion of the transceiver. The reason for this is that there has been little or no interest shown by readers of my blog, so I quit posting some time ago. Yours is the first comment I have received since moving the blog from my original”WannaTinker” blog many months ago. Unfortunately, the WannaTinker blog no longer exists.

      Having said that, I will add that I will be happy to send additional information about the WT40 transceiver via email. I have your email address, and I will try to find the calibration information for the VFO and send it to you within the next few days.

      Thank you for your interest in the WT40. Building it is a long and tedious process, especially if you are new to constructing electronic circuitry, but the reward is being able to tell the guy on the other end of the QSO “The rig here is home brew – from scratch.” and mean it. Besides that, messing about with components, tools, and test gear is quite a pleasure for those of us who enjoy that sort of thing.

      73,
      Clint, W6BKY

      • oscar says:

        Hello Clint. Do not worry, you are not alone! In this silent congregation there must be hundred of people interested but perhaps too lazy to write for a few minutes. I have built your initial project, just for fun and in order to keep my “hands in” with the soldering iron and the “old” RF. I was an OM until the 90s and I left my licence expire(GW5CLY) because of work load. Now I have been retired for the last 5 years but I have never forgotten the thrill of new electronics challenges, I have built hundreds of tx s and rxs during my ham life, The only items I have ever bought was an old 1155…keep up the good work if you can(it saves digging the garden and mowing the lawn….Hope I have not
        bored you, 73, Oscar

  2. Little or no interest?!
    I can’t believe that.
    This is information is GOLD!
    .I have been searching for this kind information FOREVER.
    I don’t know how I found this blog but when I did,the clouds parted with sun shinning through and Ole to Joy blasting from the heavens LOL
    Everything is written in layman’s terms
    Exactly how I like it!
    I am going to be picking your head until it hurts
    LOL

    Carl
    KD8GLK

  3. w6bky says:

    Carl,
    Thanks for the flowers !!
    You will be receiving an email with additional information soon.

    FYI: I have discovered a problem with the backup files on this computer. I am trying to sort out the problem and get it fixed, if possible. In any event, it appears that many, if not all of the backup files are simply gone, and it may take me a while to regenerate the material. I think this was caused by a recent “update” that I installed a while back – – it seems that the “improvements” have rearranged virtually everything about the operating system and I am now climbing yet another learning curve in order to do word processing and/or graphics with the computer.

    Why can’t they simply quit fixing things that are not broken ??!! Everything had been working just fine until the “upgrade” was applied.

    Oh well . . . that’s life with computers, I suppose.

    73, Clint, W6BKY

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