Practical Hints and Tips
March 9th, 1932 The Wireless World Article
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.
articles are scanned and OCRed from old editions of The Wireless World magazine.
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
See all the available
The Wireless World articles.
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
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.