These articles are scanned and OCRed from old editions
of The Wireless World
I finally managed to get an early edition of The Wireless World magazine for a reasonable
price on a eBay auction. Now I will be able to post a few of those articles from the UK to
compliment those from some of the American magazines. This particular edition is from March
9th, 1932. My next target is to get a few from the World War II era which although it began
on December 7, 2941 from America's perspective, it officially began on September 1, 1939 for
Warning for the weak of heart - epochal words like "niggardly" and
"parsimonious" are used herein, and therefore adult supervision should be employed if ignorance
might cause an objection to at least one of the aforementioned.
See all the available
The Wireless World
Practical Hints and Tips
Simplified Aids to Better Reception
When a receiver is fed with H.T. current
from the mains, there is no particular need to be niggardly in the matter of consumption;
a few milliamps. here or there make practically no difference to the cost of upkeep. But it
is a different matter when dry batteries are employed; in this case, all possible sources
of waste should be rigorously avoided, and it may be helpful to enumerate some of the more
common causes of excessively high anode current.
As often as not, a valve takes more
anode current than it should because an insufficient amount of negative bias is applied to
its grid. Of course, the same thing happens if the grid is totally unbiased, but then an audible
indication that something is wrong is generally given. Further, it is not enough that merely
the bias battery itself should be in order, and where there arc grounds for suspicion, it
is advisable to test the entire circuit for continuity to make sure that a negative voltage
is actually impressed on the grid.
A "soft" valve will generally pass a high anode
current ; if this defect is not made obvious by the presence of a blue glow around the electrodes
of the valve. it may generally be detected fairly easily by short circuiting the grid circuit
resistance, and noticing whether this brings about an appreciable change in anode current.
If it does, the valve will definitely be "soft." It should be remembered that if there is
not already a resistance of sufficiently high value in the grid circuit, this test will not
be conclusive, but a resistance may be temporarily inserted.
Other faults that may
occasionally be responsible for excessive anode current consumption in battery-operated sets
are short-circuited anode feed resistances, or leakages. or more or less complete "shorts"
in the anode circuits; the bypass condensers may be suspected.
Users of D.C. mains
supplies are always handicapped by the fact that the H.T. voltage available is inevitably
fixed at a considerably lower value than that obtainable from the majority of A.C. rectifiers.
This limitation is particularly annoying when one is trying to devise means for supplying
a power grid detector with sufficient anode pressure; even if initial difficulties are overcome
the detector decoupling must always be designed on almost parsimonious lines. Even if
actual "motor-boating" is not present, there is always an uneasy feeling that too much stray
L.F. reaction for really good quality is taking place. The final result is that we generally
arrive at a compromise something like a "semi-power grid" detector, in which the usual anode
circuit limitations may possibly become evident, due to insufficient H.T. voltage. At the
best, we can hardly hope to use, as a coupling between the detector and succeeding L.F.
valve, an arrangement which will produce anything approaching the maximum attainable magnification.
The type of diode detector discussed in The Wireless World of February 3rd suffers
from none of these limitations, and, apart from providing almost perfect detection, has the
additional advantage that it does not impose any serious damping on the tuned circuit which
immediately precedes it. The arrangement, therefore, is one that should be particularly attractive
to D.C. mains users, who may accordingly be interested in the skeleton circuit diagram given
in Fig. 1. This shows the nucleus of a diode - a L.F. set suitable for high-quality reproduction
of local broadcasting, and in which indirectly heated D.C. valves are used throughout. Where
greater range is necessary, an H.F. stage may be added in' the usual way.
In the suggested
circuit diagram a pentode output valve is shown, but, of course, there is. no reason why this
should not be replaced by a triode, or where large outputs are required, by a pair of triodes
A set on these lines, with an H.F. amplifier. is definitely capable of
long-distance reception, and there is always the possibility of improved sensitivity by using
the diode anode -which in the simpler form of circuit is unemployed-for purposes of reaction
in the manner suggested in The Wireless World of June 10th, 1931.
Posted April 4, 2011