DESCRIPTION
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 have aged.

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
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.

SWITCH OPTIONS
S1-A    OFF = 100Hz Resolution    ON = 1KHz Resolution
S1-B    Turn ON To Select The TWEAK MODE To Calibrate For Accuracy
S1-C    Not Used
S1-D    Interface Power

TWEAK MODE
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.

LOW ADJUST
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.

HIGH ADJUST
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
Operation is automatic.  There are no operating instructions.