[ARC5] Drift in BC-453 - more

[Ian Wilson]

1MHz / 200 -> 5kHz (pair of cascaded 74LS90's); pick off 17th harmonic with
an LC.

A rather better idea would be to use a DDS. Good accuracy but not sure
about the jitter.

73, ian K3IMW



On Wed, Dec 13, 2017 at 9:02 AM, John Hutchins <jphutch60bj at gmail.com>
wrote:

> Watching the conversation take shape over time:
>
> If the tube is the culprit in MO drift,  I may have miss remembered,  I
> read some where that regulating the filament voltage to the M.O. 6J7 ... ,
> and the Detector (12,6)K8 may help in subduing the tube drift, do to
> changes in temperature do to voltage swing.   True or not true?
> Thanks
> Hutch
>
>
> On 12/13/2017 9:54 AM, J Mcvey via ARC5 wrote:
>
> I have been musing about the "why" of VT oscillator instability. OK,
> there's definitely a thermal element, but what parameters of the tube are
> most affected?
> I checked the spec on the resonating cap for the BFO and it is +/- 2 pf !
> So the tube must be the culprit.
> Not being from the vacuum circuit design era, I took a look at some texts
> on the subject. It looks like the solution can become quite complex if one
> desires tight VT stability specs.
>
> I'm going to put a cheezy Cmos LC oscillator together and let it run a
> while to see what kind of drift it produces.
> There were some 1 Mhz clock modules in the junk box, but there is no clean
> integer divide down that will arrive at 85Khz...dang!
> Maybe a 455 Khz resonator oscillator can be padded down to 425 Khz so it
> can be divided by 5? Or will that cause instability- on not work at all?
> Has anyone here tried heavy padding of a resonator? Did it work Ok?
>
>
>
> On Tuesday, December 12, 2017 8:56 PM, Kenneth G. Gordon
> <kgordon2006 at frontier.com> <kgordon2006 at frontier.com> wrote:
>
>
> On 12 Dec 2017 at 0:00, spr at earthlink.net wrote:
>
> > Yes, but it doesn't have the truly horrible AVC LO frequency pulling
> that 6A7and 6A8 have.
>
> True, but both of those were early tubes that the 'K8 was supposed to
> supplant.
>
> > >
> > >6/12K8 is the absolutely noisest "converter" tube in Terman's entire
> long list. I hate the thing
> > >for that, but it does work well enough in the "ARC-5" receivers....
> > >
> > >Ken W7EKB
> >
>
>
>
>
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