EMRFD Message Archive 4124

Message Date From Subject
4124 2010-01-31 14:04:48 davidpnewkirk Reference: Hartley oscillator inductance based on 2 not-coupled coil
Earlier this month, a new free-for-the-download reference appeared in Pete Millet's Technical Books Online pages (http://www.pmillett.com/technical_books_online.htm): William A. Edson, "Vacuum Tube Oscillators" (New York: John Wiley and Sons, 1953). The download link is http://www.pmillett.com/Books/vto.pdf.

Browsing for new details on familiar circuits, I found a seconding of EMRFD's mention (in "Variations on the Simple Hartley," page 4-6, and also Figure 4-7) that Hartley oscillators can be constructed using a "tapped" coil consisting of two separate, *not*-coupled coils. Many of us have likely happened on that understanding through experiment--even though the operation of the tapped inductor in a classical Hartley is commonly described in terms of autotransformer action. Now we have a reference on such operation from over half a century ago. Writes Edson on page 168:

"The circuit will operate if there is no mutual inductance between the two sections of inductance. However, it is much simpler to construct the coil as a single continuous tapped winding, and this is almost always done because the overall efficiency and performance are considerably improved thereby. The coupling coefficient between the two sections of the coil should be made as large as possible, because the leakage may be represented as an inductance in series with the cathode lead. Such an inductance interferes with efficient class C operation."

Best regards,

4136 2010-02-01 09:07:50 Harold Smith Re: Reference: Hartley oscillator inductance based on 2 not-coupled
On the other hand, folks who like to try out oscillators in SPICE will find
it easier to set up a Hartley with non-coupled inductors. They can also
often be easier to homebrew and adjust in hardware, since moving the tap on
a coil can be tricky, especially a toroid.

de KE6TI, Harold Smith