The DD-101H Digital Dial installs in all Hammarlund models that have an
opening for a clock, and provides digital readout to 100Hz
resolution. A TCXO is used for the reference frequency which
makes the dial highly accurate and stable. The DD-101H is
potentiometer programmable for any Hammarlund model. Operation is
automatic, there are no controls. The dial can be
calibrated to compensate for receiver misalignment or crystals that
MOUNTING THE DIAL
1) Remove the clock or hole cover plate.
2) Screw the small metal plate to the back of the
front panel using the lower clock mounting holes while aligning the
large hole with the hole in the panel. Don’t tighten the screws
all the way yet.
3) Insert the display panel between the receiver
front panel and the small metal plate and tighten the screws.
Don’t worry if it is a little crooked, you can straiten it later.
4) Next mount the electronics module to the receiver
using the top clock mounting holes. Check that the display is
strait and tighten all of the screws.
5) As viewed from the front of the receiver, route
the display ribbon cable to the right under the electronics module,
then up the right side, and plug it on to the 14 pin connector on the
electronics board. If the red stripe is at the top of the display
module, it will be toward back of the receiver. Plug the RED RCA
plug into the RED RCA jack on the electronics board.
Power for the dial is from the 6.3VAC filament supply, or 9 to 12VDC
can also be used.
The power cable has a red and a black alligator clip. To connect
to the 6.3VAC supply without soldering, the insulation on one of the
wires going to the receiver’s dial lamps can be removed just enough to
allow the red alligator clip to be attached. The black clip
should be grounded.
A better way is to remove the alligator clips, route the cable under
the chassis, locate a 6.3VAC source, and make a solder
connection. The wire with the stripe is the power wire.
Ground the wire without the strip.
CAUTION, REVERSING THE CONNECTIONS
WILL SHORT THE 6.3 VOLT SUPPLY AND WILL DAMAGE THE RECEIVER.PROGRAMMING
Adjust potentiometer R7 (BLUE DOT) until the dial reads your
model number, then turn it a little more.
COUPLING TO THE VFO
Included with the DD-101H is an interface circuit and tube shield
assembly. The assembly uses the capacitance between the tube and
the tube shield to couple the VFO signal to the DD-101H.
Plug one end of the twisted cable into the interface circuit and the
other end into the black RCA jack on the electronics board. Remove the
tube shield from the HF oscillator tube, usually V2, and replace it
with the tube shield and interface circuit assembly provided with the
DD-101H. Don't push it all the way down. It must not ground
to the chassis. Clip the BLACK wire to ground. Adjust the level
control R4 for a stable display over the desired range. Switch D
of S1 is interface power and must be ON.
S1-A OFF = 100Hz Resolution ON =
S1-B Turn ON To Select The TWEAK MODE To Calibrate
S1-C Not Used
S1-D Interface Power
The tweak mode is used to calibrate for inaccuracy of your receiver’s
IF frequency. Unless you require extreme accuracy, this
adjustment will probably not be necessary. There is a High and a
Low adjustment. If your receiver is a single conversion, the Low
control is the only adjustment that applies. The High adjustment
is for double or triple conversion models.
Peak the receiver on a known frequency below 7MHz. An AM
broadcast station will work on general coverage receivers. Now
adjust the Low adjustment, R5 (GREEN DOT) for the correct reading on
the DD-101H. Do this on all receivers.
If your receiver is double or triple conversion, repeat the above
procedure using WWV on 10, 15, or 20MHz and adjust the High adjustment,
R6 (RED DOT).
Operation is automatic. There are no operating instructions.