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 Europe.
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
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
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
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 push-pull.
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