Radio Construction

Radio Record, Volume III, Issue 26, 10 January 1930, Page 31

Radio Construction

Successful. -Models H continually receive comments from listeners*’concerning the models that have been described in the "Revord" and made up'by them. There are many who ‘encounter difficulties which we can usuaHy trace to some _ little fault committed by themselves, Probably the most outstanding successes we have had. have been the "B and O" eliminator. described in the "Radio Listeners’ Guide," "Pentode's" Dynamic Cone Speaker, the Linen Diaphragm Speaker, -CRound-the-World" Lwo, and the Browning-Drake reteiyers, Following are the results of two constructors 'who have communicated with us recently, wats , "TY have successfully. constructed a "B" eliminator to the specifications given in the "Radio Listeners’ Guide." I have varied slight!y from the instructions as regards transformer and chokes, The result is that the voltage is slightly higher. ‘I consider the task of building a very simple one and not above the capabilities of the. average journeyman, Providing a little patience is used in winding the transformer, which I consider the hardest part of the task, the-rest is easily built, Tt is not costly, for, I constructed my whole outfit for less than £5. I have used a wire-wound resistance with slides for the ‘tappings; in my case these are 16 volts,.90 volts, and 185 volts, The bar has been mounted on a piece of bakelite panel and the slides arranged in 1 sitiom’ and connected up. I had the eliminator working within an hour after Having: received the resistance bar, which goes to show the simplicity of this type of confrol unit. The cost is approximately 15/- complete. The voltage can be varied to 2-Volt if necessary. I advise any listener who desires a power pack and has afew spare evenings not, to be afraid of undertaking the construction. of this one. All necessary data is given ‘in the "Listeners’ Guide." It is all very simple and easy to follow. . This is especially so when using’ the Ratheon valve.’ The commercially-made power packs are excellent, but their cost, in my opinion, is rather prohibitive to the man who has the patience-to: build his own. To

get good results one needs an output of 180 volts and 60 milliamps., and this, can be delivered by this outfit in question."-§, Ellis (Nelson), This has evidently been a very successful description, for we know of ‘several other satisfied constructors. We have seen one very fine eliminator, the workmanship of Mr, H. R, Simmonds, of Khandallah, The instructions in this case were followed to the letter, with the exception of the arrangement of the components in the tin, case. The condensers were not put underneath, but arranged so that they could be reached with ease. Grid bias has been provided by means of a Wire-wound resistance of 2,000 ohms, which gives the requisite 40 volts for a 171 or smaller voltage for other types of power valves. A.C, filament voltage has been provided and lights the power valve, and there is no hum. This constructor has also built "Pentode’s" dynamic cone speakér, and as we have hear¢ this working, and have compared it with our standard model, we must compliment him on the very fine job he has made of it, Realising the popularity of this Speaker, we shall describe it again in a future issue, embodying the improvements used by Mr. Simmonds, In the meantime, we should like to hear from ° other constructors who have had difficulty or success, so that these cases may be dealt with in the re-description, One of the most successful receivers we have published has been the shortwave "Round-the-World" Two This fine little receiver has been built by a yery large number of constructors, and to the credit of all concerned, we have received communication from only one correspondent who encountered difficulty, and this was through not following the specifications ona vital point,