April 1952 QST
Table of Contents
articles are scanned and OCRed from old editions of the ARRL's QST magazine. Here is a list
of the QST articles I have already posted. All copyrights are hereby acknowledged.
We live in days of plenty of everything. People throw away
and stash away items that our parents - and particularly grandparents - could only dream of having available.
Even households that have never seen a penny of earned income in decades are overflowing with stuff.
Shopping carts in Walmart, K-Mart, and Target are filled to overflowing when I am there with toys, shoes
and clothes, electronic gadgets, sporting goods, automotive accessories, pet food
(Target has reefers with fresh meat for dogs) and accessories, lawn and
garden implements, hand tools, DVDs and Blu-rays, televisions, disposable diapers (lots of disposable
diapers), snack cakes and crackers, soda, bottles of - get this - water (that
costs as much as soda), ice cream, frozen pizzas and microwaveable dinners, energy bars and bags
of candy. You get the picture. People have so much stuff that one of the largest areas of the store
is the plastic storage bin section - reserve one for each giant, electric fan-inflated Christmas or
Halloween lawn ornament. This mid-twentieth-century tongue-in-cheek anecdote is not so far from how
many - maybe most - people lived at the time.
Stretching the Junk Box
How to Make Use of Leftovers
By Robert G. Seymour, * W9WJS
In this little yarn, W9WJS presents a graphic picture of the problems of a ham who is low on cash
and yet isn't sure just how far he can go in making substitutions from the junk box. After reading it,
perhaps you'll find that you can build that new piece of gear after all.
A recent article1 in QST described in some detail the things to be taken into consideration
when building a transmitter. While the information given was very useful, it did not treat what is often
more of a problem to many of us; that is, how to stretch what we find in the junk box to cut the cost
to a minimum.
transmitter I build is a modification of some original circuit taken from a handbook or magazine article.
Let us consider the procedure after deciding to build the same transmitter which was described by Goodman
in the original article. We have decided that this rig is the one that will most closely fit our needs
and the one whose parts we most likely have on hand. We like the idea of including a crystal switch
so a look through our stock of switches reveals that we have one that will do, but it has only three
contacts. So, holding our breath we look in the tin can where we keep our dimes and quarters which we
laughingly call "radio money." Having already looked in the catalogs we find that the money on hand
is enough to cover the cost of a switch, providing no other new parts are required.
Laying aside the question of the switch for the moment, we go on to the other parts requirements.
Small parts, such as resistors, are already on hand. Of course, they have been used in numerous other
pieces of equipment and the pigtails are a little short, but that problem can be taken care of by soldering
on extensions. The values may not be just what the circuit calls for, but with a little luck we can
get by with a few substitutions if they are fairly close. For instance, if we do not have a 47,000-ohm
resistor a 56,000-ohmer might do. The only way to find out is to try it in the circuit. If the circuit
calls for a 0.005-μfd. capacitor and one cannot be found in our stock of parts, a 0.004 will do -
we hope. At any rate we can forget about the small parts until the rig is built and tested, then, if
it does not perform the way the article says it should, we can start to suspect our substitutions.
Now we compare the larger parts listed for the circuit with what we have in the junk box. This rig
requires two variable capacitors, both 300 μμfd. After a little searching one is found, but it
is only 150 μμfd. However, by winding the coils properly, this can be used on 80 and 40 meters,
which are the two bands to be used, anyway. But we still need another one. Shall we use the money to
get a variable capacitor and forget about switching crystals? Well, let's wait a while before deciding
and go on to the other parts required.
What other parts do we need? Well, the circuit shows a 150-ma. meter. Now the only meter that does
not already do constant duty is the one in the grid-dipper. Of course, that one has only a 1-ma. scale,
but we could use it by winding a shunt for it. But now comes another problem. We do not have the coils
specified in the diagram and will have to wind our own, and it will be much easier to wind them if the
grid-dipper is in operation, especially since the capacitor on hand is not of the value specified. So
we will dispense with the meter and use a pilot lamp instead. We know we are not going to exceed the
FCC power limitation with a 6L6 and a pilot lamp will tell us when the circuit is tuned to resonance
and tell us if the antenna is loading the circuit.
Now the only thing left is a couple of r.f. chokes, and, lo and behold, here is a brand-new one.
Wonder where that came from - must have swapped somebody something for it. That leaves only one choke
that we need. Now let's see - there were a couple of chokes in that portable rig that was built to take
on vacation last summer. Won't be needing it again until next year and, anyway, if this rig works OK,
we can take it on the trip. So now we get out the destruction tools, a pair of cutters and screwdriver,
and go to work on the portable. What's this? Here is another variable capacitor, and just what we need.
We do not know what the capacitance is but it tuned 80 in this rig so guess it will work OK in the new
We can now go back to the problem of the crystal switch. Everything else has been taken care of and
the money is still in the tin can. Just how advantageous would it be to have that switch in the circuit?
Well, with the switch we can QSY in a second or two unless we make a big change in frequency. If we
do that we would have to retune the final and antenna tuner which would take - oh, maybe ten seconds.
We could probably change crystals by hand in eight or ten seconds, and another ten seconds to retune
if necessary. Of course, this is assuming that we can find the crystals, so we would have to make a
point of keeping them handy. So, by using the crystal switch, we can save a maximum of ten seconds or
so. Is it worth it? I don't think so. Besides, we will need a couple of beers while sweating out the
actual construction, and the "radio money" would come in very handy for that purpose.
next problem is how to fit the parts in and around the holes already on the chassis we found in the
junk box. It would be nice to start out with a clean chassis, but we are already using parts that have
been used and reused, so why change now?
The thing to do is to choose the chassis with the fewest holes, or the one with the holes most nearly
in the proper places. Having done this, we begin. But wait - how about a panel? Let's look back at the
article and see what has to be mounted on the panel. Just two tuning knobs, a meter and a key jack.
Remember, we have decided not to use a crystal switch, so that will not have to be mounted. We are not
using a meter, so the only things left are the two knobs and the jack. The jack and the pilot lamp can
be mounted on the lip of the chassis, and the knobs can be mounted directly on the capacitor shafts.
So we don't need a panel, and besides, we would have to do without a couple of beers if we wanted to
buy one. No panel.
Now, using the available holes in the chassis, we start laying out the rig in the way it is to be
constructed. Following the accepted practice of making all leads as short as possible, we can use most
of the holes. If a hole does not line up where we want it, we can punch another one - one more won't
make any difference in the appearance. But we try to use as many of the existing holes as possible because
it saves a lot of work. We want to keep away from making any more large holes because we would have
to borrow a socket punch, which, of course, we do not have.
Because we have used this system of utilizing existing holes, we do not have to worry much about
the placement of the small parts. They will just have to go in the space available. One thing we must
try to do, however, and that is to avoid placing the parts in more than one layer. The reason for this
is that, if when testing the rig a change has to be made, the parts are much easier to get at if they
are in only one or two layers.
turning on the power we check our wiring against the diagram to be sure we have made no mistakes. Remember
that we have made some substitutions and that what may appear to be a mistake in wiring may not actually
be so. Now we plug in the oscillator tube and crystal and turn on the power. Listen to the receiver
on the frequency of the crystal. If we hear the signal from the oscillator, we plug in the 6L6 and the
final tank coil. After a suitable warm-up we should get an indication on the pilot lamp. But the lamp
does not glow. Well, let's try another 6L6 first. Oh, oh. We don't have another. Well, temporarily we
can swipe the 6F6 out of the receiver. Now everything is fine, except the pilot lamp will not show a
dip in plate current. So now we get out the grid-dipper and find that the frequency of the tank circuit
is too low, so we remove a few turns from the coil and try it again. Now we get a dip in current and
are ready to connect the antenna. The antenna seems to be loading up properly, so the only thing left
is to check the quality of the signal in the receiver.
But now the receiver is inoperative because the output tube is being used in the transmitter. Let's
see, the d.c. receiver upstairs has a pair of 6V6s in the audio, and we could probably borrow one without
anyone knowing about it. So we get one of the 6V6s and put it in the transmitter, return the 6F6 to
the receiver and check the signal. Everything seems to be working fine.
So now we have a new rig ready to try on the air and the beers that we bought with our "radio money"
helped us get through the construction and testing without too much trouble.
1 Goodman, "How to Lay Out a Transmitter," QST, July, 1951.
Posted July 12, 2016