How to add crystal oscillator to S-108?
 

I've had an old Hallicrafter's S-108 since the early 70's, and trying
to tell what freq I'm on is impossible. Does anyone know of a method for
installing a crystal oscillator on this old tube rcvr, or some other method
of acurately determining which frequency the radio is receiving at the
moment?
Many thanks for the help!

--
Allen McBroom
www.NPSTKD.com
Remove WOOF when replying by email

"Allen McBroom" wrote in message
. 97.132...
I've had an old Hallicrafter's S-108 since the early 70's, and trying
to tell what freq I'm on is impossible. Does anyone know of a method for
installing a crystal oscillator on this old tube rcvr, or some other
method
of acurately determining which frequency the radio is receiving at the
moment?

The old classic way was a 100KC crystal calibrator.

More modern displays sample the VFO, add in the IF and display the count.

Many thanks for the help!

--
Allen McBroom
www.NPSTKD.com
Remove WOOF when replying by email

It would be easier by far to build (or buy) your own external oscillator.
This will not only work with your S-108 but with anything else you might buy
down the road, and you won't have to hack holes in your radio. The basic
one is just a crystal oscillator with a 100kHz crystal. Fancier ones will
allow you to switch in a 1MHz crystal. I have an old Heathkit one that I
hopped up by adding a divider to get marks at 100, 50 and 25kHz for aligning
narrow-spread QRP receivers.

I know that any ARRL Handbook from 1930 to 1976 will have such a circuit --
I'd be mildly surprised to find out that a later one lacked it, but I'm too
lazy to get up right now and check. The 100kHz crystals are still available
from places like JAN Crystals and International Radio
(http://www.qth.com/inrad/). You can pretty much decide what you want the
thing to look like, select the appropriate date handbook and start cutting
metal.

"Allen McBroom" wrote in message
. 97.132...
I've had an old Hallicrafter's S-108 since the early 70's, and trying
to tell what freq I'm on is impossible. Does anyone know of a method for
installing a crystal oscillator on this old tube rcvr, or some other
method
of acurately determining which frequency the radio is receiving at the
moment?
Many thanks for the help!

--
Allen McBroom
www.NPSTKD.com
Remove WOOF when replying by email

"Tim Wescott" wrote in message
...
It would be easier by far to build (or buy) your own external
oscillator.
This will not only work with your S-108 but with anything else you
might buy
down the road, and you won't have to hack holes in your radio. The
basic
one is just a crystal oscillator with a 100kHz crystal. Fancier ones
will
allow you to switch in a 1MHz crystal. I have an old Heathkit one
that I
hopped up by adding a divider to get marks at 100, 50 and 25kHz for
aligning
narrow-spread QRP receivers.

I know that any ARRL Handbook from 1930 to 1976 will have such a
circuit --
I'd be mildly surprised to find out that a later one lacked it, but
I'm too
lazy to get up right now and check. The 100kHz crystals are still
available
from places like JAN Crystals and International Radio
(http://www.qth.com/inrad/). You can pretty much decide what you want
the
thing to look like, select the appropriate date handbook and start
cutting
metal.

There's also plans for crystal calibrators on the net. Here's one:

http://www.rason.org/Projects/calibrat/calibrat.htm

Frank Dresser

I would simply use a divide by ten oscilloscope probe
connected to the plate of the S-108 local oscillator tube, feeding
a frequency counter. The divide by ten probe provides isolation,
to avoid pulling the oscillator off frequency.

If you just want a 100 KHz calibrator, I recommend an old Bud Radio
model "FCC-90 B". It has it's own power supply, and requires
no connection to the receiver. (Just uses a loosely coupled
antenna wire near the receiver input). It has two tubes,
a 35W4 and a 50C5, in a transformerless circuit.
The older Bud model FCC-90 used octal tubes.

73,
Ed Knobloch

Allen McBroom wrote:
I've had an old Hallicrafter's S-108 since the early 70's, and trying
to tell what freq I'm on is impossible. Does anyone know of a method for
installing a crystal oscillator on this old tube rcvr, or some other method
of acurately determining which frequency the radio is receiving at the
moment?
Many thanks for the help!

Edward Knobloch wrote:
I would simply use a divide by ten oscilloscope probe
connected to the plate of the S-108 local oscillator tube, feeding
a frequency counter. The divide by ten probe provides isolation,
to avoid pulling the oscillator off frequency.

If you just want a 100 KHz calibrator, I recommend an old Bud Radio
model "FCC-90 B". It has it's own power supply, and requires
no connection to the receiver. (Just uses a loosely coupled
antenna wire near the receiver input). It has two tubes,
a 35W4 and a 50C5, in a transformerless circuit.
The older Bud model FCC-90 used octal tubes.

73,
Ed Knobloch

While all of the previous comments are good advice I suspect a counter
would drive a guy crazy on an S-108 with the constantly drifting freq
and oscillator pulling.
The 100kc calibrator will get you in the ballpark...at least to as close
as you can read the dial...I don't recall that there's a front panel
tweak to align the pointer or LO to have the calibrator line up with the
dial.
Nice little radio but if you want a better radio, well...
Its kinda like sticking STP racing stickers on a Chevy Vega.

-Bill

"-Bill M-" exray@coquidotnet wrote in message
...

While all of the previous comments are good advice I suspect a counter
would drive a guy crazy on an S-108 with the constantly drifting freq
and oscillator pulling.
The 100kc calibrator will get you in the ballpark...at least to as
close
as you can read the dial...I don't recall that there's a front panel
tweak to align the pointer or LO to have the calibrator line up with
the
dial.
Nice little radio but if you want a better radio, well...
Its kinda like sticking STP racing stickers on a Chevy Vega.

-Bill


The bandspread is marked off with a 0 - 100 interval. If the operator
notes the number of bandspread divisions between known 100 kc intervals,
he can come up with a reasonably precise approximation of the actual
frequency. Good enough for SWLing, anyway.

Frank Dresser

Frank Dresser wrote:
"-Bill M-" exray@coquidotnet wrote in message
...

While all of the previous comments are good advice I suspect a counter
would drive a guy crazy on an S-108 with the constantly drifting freq
and oscillator pulling.
The 100kc calibrator will get you in the ballpark...at least to as

close

as you can read the dial...I don't recall that there's a front panel
tweak to align the pointer or LO to have the calibrator line up with

the

dial.
Nice little radio but if you want a better radio, well...
Its kinda like sticking STP racing stickers on a Chevy Vega.

-Bill



The bandspread is marked off with a 0 - 100 interval. If the operator
notes the number of bandspread divisions between known 100 kc intervals,
he can come up with a reasonably precise approximation of the actual
frequency. Good enough for SWLing, anyway.

Frank Dresser



I suppose so. On a 'factory aligned" job one still might have to
struggle with which 100kc blip is which.

-Bill M

Edward Knobloch ) writes:
I would simply use a divide by ten oscilloscope probe
connected to the plate of the S-108 local oscillator tube, feeding
a frequency counter. The divide by ten probe provides isolation,
to avoid pulling the oscillator off frequency.

If you just want a 100 KHz calibrator, I recommend an old Bud Radio
model "FCC-90 B". It has it's own power supply, and requires
no connection to the receiver. (Just uses a loosely coupled
antenna wire near the receiver input). It has two tubes,
a 35W4 and a 50C5, in a transformerless circuit.
The older Bud model FCC-90 used octal tubes.

73,
Ed Knobloch

Nobody has to go back that far. You can go back thirty to thirty five
years, and crystal calibrators were solid state. Not just that, but
they had a divider so you could get multiple outputs. This is
real useful for the especially ill-calibrated receiver (start witha
1 MHz output because they are easier to count), and those 25KHz outputs
were useful even for the better calibrated receivers, to find those subbands.

And realistically, once transistors and then digital ICs became available,
crystal calibrators were amongst some of the first station accessories to
be turned solid-state. And they were applied at the time to many a
real boatanchor.

Michael VE2BVW

Allen McBroom wrote:
I've had an old Hallicrafter's S-108 since the early 70's, and trying
to tell what freq I'm on is impossible. Does anyone know of a method for
installing a crystal oscillator on this old tube rcvr, or some other method
of acurately determining which frequency the radio is receiving at the
moment?
Many thanks for the help!

"-Bill M-" exray@coquidotnet wrote in message
...


I suppose so. On a 'factory aligned" job one still might have to
struggle with which 100kc blip is which.

-Bill M


Not to mention images and unmodulated carriers. Actually, I never used
a crystal calibrator. I'd count off the divisions between two known SW
broadcasters and divide difference in frequency by the number of
divisions and come up with a useful approximation. It's kind of a pain.
And not so useful for the ham bands. Anyway, I haven't done it in
years, and I never did it much. I mostly listen to the strong domestic
SW stations now.

Those non-linear bandspread capacitor plates on the S-38 and S-53 types
will introduce more errors.

Frank Dresser