02-09-2014, 11:22 PM
Alan - I quote from the ARRL Handbook, 53rd. edition, 1976, page 137:
The power available (from a crystal oscillator) is limited by the heat that the crystal will stand without overheating. The amount of heating is dependent upon the r.f. crystal current, which, in turn, is a function of the amount of feedback necessary to provide proper excitation. Crystal heating - short of the danger point - results in frequency drift to an extent dependent upon the way the crystal is cut.
► Note that last bit, highlighted in blue (by me): I read that to be an indirect reference to an X-cut.
And on page 138:
Crystal current may be estimated by observing relative brilliance of a 60-mA dial lamp connected in series with the crystal. Current should be held to the minimum for satisfactory output by careful adjustment of excitation. Typical crystal currents should be in the vicinity of 40 mA.
On both those pages, there are various cct. diags. of crystal oscillators - but in none of them does the 'dial lamp in series with the crystal' actually appear.
OTOH, not all of the ccts. thus shown are valved-based; some use bipolar transistors - and at least one is shown using a F.E.T.
Personally, I reckon several chunks of those extracts were simply copied from the previous edition of that book, which were copied from an earlier edition, which were copied . . . . ad nauseum . . . and possibly right back to edition #1 !
In which case, the editorial attitude must have been "If in doubt, leave it in". 
Al. / Sept. 3, 2014 //
The power available (from a crystal oscillator) is limited by the heat that the crystal will stand without overheating. The amount of heating is dependent upon the r.f. crystal current, which, in turn, is a function of the amount of feedback necessary to provide proper excitation. Crystal heating - short of the danger point - results in frequency drift to an extent dependent upon the way the crystal is cut.
► Note that last bit, highlighted in blue (by me): I read that to be an indirect reference to an X-cut.
And on page 138:
Crystal current may be estimated by observing relative brilliance of a 60-mA dial lamp connected in series with the crystal. Current should be held to the minimum for satisfactory output by careful adjustment of excitation. Typical crystal currents should be in the vicinity of 40 mA.
On both those pages, there are various cct. diags. of crystal oscillators - but in none of them does the 'dial lamp in series with the crystal' actually appear.
OTOH, not all of the ccts. thus shown are valved-based; some use bipolar transistors - and at least one is shown using a F.E.T.Personally, I reckon several chunks of those extracts were simply copied from the previous edition of that book, which were copied from an earlier edition, which were copied . . . . ad nauseum . . . and possibly right back to edition #1 !
In which case, the editorial attitude must have been "If in doubt, leave it in". Al. / Sept. 3, 2014 //
