[ARC5] [Glowbugs] "Using Defective Crystals" 1937

[Dennis Monticelli]

This osc circuit places the quartz crystal in parallel resonance mode.
Feedback for oscillation is not well defined in this circuit configuration;
it is primarily from the grid-to-plate capacitance.  Working against the
crystal's inductance it produces the necessary phase shift for oscillation.

If the crystal has low activity it may not oscillate with the feedback
parameters of the circuit.  Adding some additional feedback in the correct
phase can help induce oscillation.  Multiple ways to do this.  Adding a
coil in the grid circuit that loosely couples to whatever tank coil is in
the plate circuit is one way.

But if the rock is cracked it probably received too much excitation in the
first place, which was a common problem back then in triode oscillators.
 There is no series #49 lamp to judge the crystal current.

Yes, the older crystals had their dominant resonance mode determined by
thickness.

Dennis AE6C

On Sun, Jun 21, 2020 at 10:29 PM Bart Lee <kv6lee at gmail.com> wrote:

>
> Some crystals are affected by electric fields (but not magnetic fields --
> or so says the wiki). So my guess is that
>
> 1) the coil puts some electromagnetic force at the desired frequency of
> oscillation into the crystal structure,
>
> 2) to which it responds mechanically at its characteristic frequency of
> vibration at or near the desired frequency of oscillation,
>
> 3) as a result of the electric part of the electromagnetic field.
>
> In effect, the coil "jump-starts" the crystal which then stabilizes the
> circuit's frequency of oscillation. A wild-assed guess?
>
> 73 de Bart, K6VK ##
>
> -- --
> Bart Lee, K6VK, CHRS, AWA, ARRL
>
> Texts only to: 415 902 7168
>
> www.bartlee.com
>
> {KV6LEE(at)gmail(dot)com} ##
>
> <http://www.LawForHams.com>
>
>
>
> On Sun, Jun 21, 2020 at 8:33 PM Roy Morgan <k1lky68 at gmail.com> wrote:
>
>> Ken,
>>
>> I am thinking you are right.  The FT-243 crystal blanks do get frequency
>> from thickness - I ground some up in frequency years ago.  Based on what I
>> have read, the behavior of quartz crystals is pretty complicated.
>>
>> I used to own one of the type shown in the article.  If I do discover it,
>> I likely will not crack the blank to see what happens !
>>
>> I have also owned one of the crystal filter crystal units from early
>> Hammarlund HRO receivers.  The quartz piece in them actually moves around
>> enough so it can rattle when you shake the thing.
>>
>> Roy
>>
>> > On Jun 21, 2020, at 11:11 PM, Kenneth G. Gordon <
>> kgordon2006 at frontier.com> wrote:
>> >
>> > On 21 Jun 2020 at 22:59, Roy Morgan wrote:
>> >
>> >> Hue,
>> >>
>> >> This is an interesting article.  I have had one of the round crystal
>> holders shown, but never took it apart.
>> >>
>> >> The business about
>> >>
>> >> "If it (the crystal) has been cracked ... possible to get several good
>> >> crystals from an inch square plate ... all of which will oscillate on
>> >> the original frequency."
>> >>
>> >> is pure baloney, based on all I have learned about quartz crystals and
>> >> how they operate.
>> >>
>> >
>> > You are probably correct, BUT, the frequency at which some cuts of
>> crystal oscillates is
>> > primarily determined by its THICKNESS.
>> >
>> > Ken W7EKB
>>
>> Roy Morgan
>> K1LKY since 1958
>> k1lky68 at gmail.com
>>
>>
>>
>>
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