26-08-2014, 04:52 PM
Yes, on the face value of what has been written, it is puzzling, isn't it?
One thought is that that 2v. 60 mA bulb is not there for the purposes of indicating crystal current by the bulb glowing - even faintly - but as a current-limiting protection device. Nominally, 2v. @ 60 mA gives a resistance of approx. 33 Ω. But then that encourages the obvious question: why not fit a 33 Ω resistor?
Moreover, I am puzzled by the book references you have listed. Although I do not have a copy of 'Amateur Radio, a Beginners Guide', a perusal of the RSGB Handbooks, 3rd., 4th. and 6th. editions do not have references to any crystal oscillator circuit which includes a bulb in that manner. So, what edition of the RSGB H/B did you read?
I even wandered through the appropriate section of 'Amateur Radio Techniques, 4th. ed., 1972, (Pat Hawker, G2VA), but to no avail. This publication is usually a good source for cct. ideas, etc., as I sure you are aware.
I looked in the ARRL Amateur Radio H/B, 36th. ed., 1959: again, nothing. Similarly, no mention of it is made in 'Radio Engineering' (1932) by F.E. Terman. (So I did go back quite a few years in terms of Radio Technology). An inspection of 'The Radio Handbook', 13th. ed., 1951, R.L. Dawley, again was no help. The cct. diag. you have presented looks decidedly of USA origin to me: that is why I checked in those USA-sources.
Al.
One thought is that that 2v. 60 mA bulb is not there for the purposes of indicating crystal current by the bulb glowing - even faintly - but as a current-limiting protection device. Nominally, 2v. @ 60 mA gives a resistance of approx. 33 Ω. But then that encourages the obvious question: why not fit a 33 Ω resistor?
Moreover, I am puzzled by the book references you have listed. Although I do not have a copy of 'Amateur Radio, a Beginners Guide', a perusal of the RSGB Handbooks, 3rd., 4th. and 6th. editions do not have references to any crystal oscillator circuit which includes a bulb in that manner. So, what edition of the RSGB H/B did you read?
I even wandered through the appropriate section of 'Amateur Radio Techniques, 4th. ed., 1972, (Pat Hawker, G2VA), but to no avail. This publication is usually a good source for cct. ideas, etc., as I sure you are aware.
I looked in the ARRL Amateur Radio H/B, 36th. ed., 1959: again, nothing. Similarly, no mention of it is made in 'Radio Engineering' (1932) by F.E. Terman. (So I did go back quite a few years in terms of Radio Technology
). An inspection of 'The Radio Handbook', 13th. ed., 1951, R.L. Dawley, again was no help. The cct. diag. you have presented looks decidedly of USA origin to me: that is why I checked in those USA-sources.Al.
