On Mon, Feb 13, 2017 at 6:41 PM, Bob Camp kb8tq@n1k.org wrote:

Attached is a plot of crystal calibrators temperature stability. Span is
roughly 65 degC.

One of the other aspects I think is intriguing is the DC PSRR of a vacuum
tube crystal oscillator. In the case of a bjt based oscillator you have the
C-V relation for depletion capacitance and the base-emitter dynamic
capacitance as a function of collector current. I would suspect that for a
one active device oscillator, tube vs bjt, a tube crystal oscillator would
be less sensitive to small power supply variations (+- 10% ). Which is a
convenient attribute for a poorly/unregulated battery supply in the vacuum
tube case. Unless filament current has an appreciable impact on frequency,
I wouldn't think so...

On Mon, Feb 13, 2017 at 4:34 PM, Mike Naruta AA8K aa8k@comcast.net wrote:

I hit the view limit... "You have view 2 pictures today, and can view 0
more pictures day."

The link for the phots is:
http://www.mods.dk/picture.php?brandid=1&model=lampkin_laboratories_/_105-b

The cal capacitor is an absolute jem. Mike's Img is attached.

I would imagine you would need a decently sized pad of paper to keep track
of all the details when measuring an unknown signal.

Just, zero-beat the 50th harmonic of the VFO -- as you do. When measuring
on the low end of the frequency scale its Mth harmonic of the DUT against
the Nth harmonic of the VFO... Plus tempCo.

Were there slide rules, pinwheels, or alternate to make frequencies
measurements a little easier?

Hi

Which eyeballs out to be pretty close to an AT. Without knowing the PPM
scale there isn’t much way to be sure.

Except you do have miller effect which pretty much messes things up
for a triode. A pentode is a bit less sensitive, but you still have issues.

Umm… errrr …. check it out :)
Oddly enough, I remember a high school physics lab where they had us plot
the effect of filament voltage on plate current and gain. Seemed like a weird
thing to do to me at the time. Turns out the teacher grew up with microwave tubes
that were tuned by varying the filament. Who knew ???  Pretty strange stuff if
you ask me.

The bigger issue is the tubes get hot. The heat varies with supply voltage.
Temperature change is the result. That temperature change messes up
oscillator stability. You pretty much have to wait for things to hit equilibrium
before you do useful stuff ( = let it warm up for an hour or four).

Bob

just be careful, because if you under-heat the cathode you could kill it

73

Alex

On 2/13/2017 7:11 PM, Bob Camp wrote:

On 14 February 2017 at 04:23, Raj vu2zap@gmail.com wrote:

Ah, a sensible, descriptive name for the unit.  Some of these modern units
really do Hert(z) :-)

 Peter

Hi

That was one of the reasons I was a bit amazed high school students
were doing it as a lab exercise. The presence of high voltage here and
there is something that you simply would not see in a similar school
today …

Bob

Taking a second look in the manual, they specifically call out that its not
an AT or BT, so I'm not sure what it would be.

Interestingly they describe the thermometer as space-saving and trouble
free alternative to a heater and thermostat apparatus (I guess they weren't
called ovens yet?)

On Mon, Feb 13, 2017 at 10:11 PM, Bob Camp kb8tq@n1k.org wrote:

HI

What frequency is the crystal and what sized package is it in?

Bob

Hi,Sorry if I caused confusion by calling the SCR/BC221 a wavemeter. Clearly it's not in the wider usage of the term, and the manual and front panel call it a frequency meter. However the similar British device was called a wavemeter "Wavemeter Class D" http://www.vmarsmanuals.co.uk/archive/724_Wavemeter_Class_D_No2_Working_Instructions.pdfSo here in the UK the 221 was often also called a wavemeter. Classic wavemeters were also available for example the Marconi TF975.
Robert G8RPI.

  From: Bob Camp <kb8tq@n1k.org>

To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Monday, 13 February 2017, 23:46
Subject: Re: [time-nuts] Vintage Frequency Measurement

Hi

With a VFO running, you have a heterodyne frequency meter. That is (at least to me)
a very different device than an absorption wave meter. I know way to put power into
a BC-221 and use it as an absorption device.

I’m not in any way saying that the LM or the 221 are less useful. They are still to this day
great little boxes. The just aren’t (by my understanding) wave meters. That term describes
a different device that works a different way.

Bob