Hank
2017-12-14 09:11:31 UTC
A few days ago we were talking about boatanchor-era test equipment. I
listed two of my most useful signal generators as a Measurements 111-B
Crystal Calibrator and a Bliley 1C Crystal Controlled Oscillator.
Both of these are fairly simple units. The 111-B puts out fixed
frequency signals at 100 Khz, 1 Mhz, and 10 Mhz. It has an RF input
that allows "whistle-stop" detection of external signals, using
headphones. This unit isn't a "service shop" unit, but if you know how
to use it effectively, it is a great help in getting a really good
alignment. There is a schematic at
http://antiqueradios.com/forums/viewtopic.php?f=8&t=282966
James Millen built a "Secondary Frequency Standard" model 90501, which
is quite similar to the Measurements unit.
The Bliley 1C is quite different. It is a cheap AC-DC unit that uses
separate crystals to generate common IF frequency signals, in addition
to 200 Khz and 1 Mhz signals for general alignment purposes. A full
manual is at:
http://www.bliley.net/XTAL/docs/manuals.html
This manual covers the earlier model 1A, as well as the 1C unit, which
is what I have.
Unlike the Measurements and Millen units, it was sold for service shop
use. All three units have internal audio modulation oscillators, but
the Bliley does not have an internal detector setup.
Used in conjunction with a VFO signal generator like a Precision 200,
you can get very precise alignments and tracking. The big pluses about
the crystal units are that the outputs are rich in harmonics, and that
the frequencies are fixed and repeatable. I got some real mileage out
of the 111-B when I rebuilt an RME-45 receiver. That is a 6-band set
that tunes 540 Khz to 33 Mhz. The first five bands use fixed padder
caps in the oscillator, all of which were shorted. Some attempts had
been made to compensate for this by spreading coil windings, and I had
considerable work to do straightening out that mess. Also, the original
padders were non-standard values, so I could only get "close." Also,
the segmented plates on the tuning capacitor needed to be set straight.
For work like this, a Q-meter and a grid-dip are very useful, but you
have to know how to use them effectively.
The real plus in using crystal signals is that you have signals at every
1 Mhz point on the dial, using the 1 Mhz output on the higher bands.
The 100 Khz. signal is more useful on the lower bands. It took some
work to conjure up the most appropriate caps to use for padding the
various bands. As a generality, the instructions for aligning a
receiver front end specify a low end about 10% up and a high end about
10% down on each band, but with spot-on signals all across each band,
you can get spot-on alignment anywhere, and check the tracking error
across the band.
The RME-45 has a crystal filter, which means that the IF's have to be
tuned to that crystal. That does require a VFO signal generator
adjusted to the filter crystal's peak. For sets that do not have a
crystal filter, like a Hallicrafters S-40, you can raise or lower the
IF frequency to improve tracking.
Hank
listed two of my most useful signal generators as a Measurements 111-B
Crystal Calibrator and a Bliley 1C Crystal Controlled Oscillator.
Both of these are fairly simple units. The 111-B puts out fixed
frequency signals at 100 Khz, 1 Mhz, and 10 Mhz. It has an RF input
that allows "whistle-stop" detection of external signals, using
headphones. This unit isn't a "service shop" unit, but if you know how
to use it effectively, it is a great help in getting a really good
alignment. There is a schematic at
http://antiqueradios.com/forums/viewtopic.php?f=8&t=282966
James Millen built a "Secondary Frequency Standard" model 90501, which
is quite similar to the Measurements unit.
The Bliley 1C is quite different. It is a cheap AC-DC unit that uses
separate crystals to generate common IF frequency signals, in addition
to 200 Khz and 1 Mhz signals for general alignment purposes. A full
manual is at:
http://www.bliley.net/XTAL/docs/manuals.html
This manual covers the earlier model 1A, as well as the 1C unit, which
is what I have.
Unlike the Measurements and Millen units, it was sold for service shop
use. All three units have internal audio modulation oscillators, but
the Bliley does not have an internal detector setup.
Used in conjunction with a VFO signal generator like a Precision 200,
you can get very precise alignments and tracking. The big pluses about
the crystal units are that the outputs are rich in harmonics, and that
the frequencies are fixed and repeatable. I got some real mileage out
of the 111-B when I rebuilt an RME-45 receiver. That is a 6-band set
that tunes 540 Khz to 33 Mhz. The first five bands use fixed padder
caps in the oscillator, all of which were shorted. Some attempts had
been made to compensate for this by spreading coil windings, and I had
considerable work to do straightening out that mess. Also, the original
padders were non-standard values, so I could only get "close." Also,
the segmented plates on the tuning capacitor needed to be set straight.
For work like this, a Q-meter and a grid-dip are very useful, but you
have to know how to use them effectively.
The real plus in using crystal signals is that you have signals at every
1 Mhz point on the dial, using the 1 Mhz output on the higher bands.
The 100 Khz. signal is more useful on the lower bands. It took some
work to conjure up the most appropriate caps to use for padding the
various bands. As a generality, the instructions for aligning a
receiver front end specify a low end about 10% up and a high end about
10% down on each band, but with spot-on signals all across each band,
you can get spot-on alignment anywhere, and check the tracking error
across the band.
The RME-45 has a crystal filter, which means that the IF's have to be
tuned to that crystal. That does require a VFO signal generator
adjusted to the filter crystal's peak. For sets that do not have a
crystal filter, like a Hallicrafters S-40, you can raise or lower the
IF frequency to improve tracking.
Hank