Note
The SB-630 was a very popular accessory containing a 24-hour mechanical digital clock, an SWR meter, a hybrid phone patch, and 10-minute timer, and made a useful and attractive addition to any station.
It’s hard to believe a gizmo like this would have tubes in it, but it does—two of them—an OA2 voltage regular and a 6EW8 relay control, both used in the 10-minute timer circuit. The timer circuit consists of an RC network that charges very slowly and fires a neon lamp. The lamp in turn sends a pulse to the grid of the 6EW8, which then conducts and closes a relay.
Depending on the setting of the TIMER function switch, the relay will activate a lamp and/or a buzzer.
Calibrating the timer to operate at 10-minute intervals is accomplished by the trial-and-error adjustment to two potentiometers—a coarse adjust and a fine adjust.
A front panel reset button restarts the timing sequence each time it is pushed. The duration of the light and buzzer is about one second.
The phone patch section is based on the HD-19, et al. The SWR meter is based on the HM-15.
The clock is a standard Numechron movement and there is no convenient way to set it. You have to reach in through the open back of the cabinet and do the best you can. After many years of operation these units sometimes start making noise, but will generally continue to work for many more years—it just depends on how long you want to put up with it. Replacement mechanisms can still be found with some digging.
The clock readout is not illuminated. The two lamps under the clock are used to illuminate the IDENTIFY sign panel.
SB-630s are occasional found with electronic digital clocks installed. If artfully done, this is a satisfactory solution. Unfortunately, this kind of modification is often accompanied by the addition of front panel switches required to set the clock. The best advice to keep the clock quiet is to only run it when you have guests in the shack. The phone patch and SWR meter will continue to work without the unit being plugged in.
Front panel controls include SWR sensitivity and forward/reverse, time reset, timer function, mode (SWR or phone patch), and phone patch receiver and transmit gain. The clock and front panel meter are not illuminated. The meter reads SWR or phone patch audio level. There is also a light that indicates when the timer is on.
Rear panel controls include phone patch null adjust, a monitor/null switch, and timer adjustment controls. Note: NULL adjustment is only required for phone patch use with VOX. PTT control does not required any NULL adjustment.
Rear panel connections include SO-239s for RF connection to the SWR meter, RCA jacks for Hi-Z or 600Ω phone patch output to the transmitter, loop-through receiver audio, and screw terminals for connection to the phone line (polarity is not important).
Note: unlike other SB-6XX accessories, the SB-630 is designed to operate only from 120 VAC, 60 Hz power (a constraint imposed by the clock motor).
References:
Review. 73 Amateur Radio. Sep 1967, p. 96.
Modification of buzzer. Ham Radio. Dec 1971, p. 75.
Digital clock modification. QST. Dec 1976, p. 42.
CLOCK / TIMER
Clock motor: 1 rpm, 120 VAC, 60 Hz, 3.7 watts
Timer interval: adjustable to 10 minutes
Timer stability: lass than 0.2% change per hour
Timer cycle: resets with pushbutton control
Timer signal: visual, or both visual and aural, switch selected
Circuit: R-C network with neon discharge and vacuum tube relay control
SWR METER
Power handling capability: 2 KW PEP
Input/output impedance: 50 or 75Ω wiring option
Band coverage: 160 to 6 meters
PHONE PATCH
Circuit: hybrid; allows VOX or manual operation; single switch control
Telephone line impedance: 600Ω
Null depth: at least 30 db separation between transmit and receive circuits
Receiver impedance: effective match from 3 to 16Ω
Transmitter impedance: 600Ω or high impedance output
GENERAL
Meter: 100 µA
Power requirements: 120
VAC, 60 Hz, 15 watts
Tubes: (1) 0A2, (1) 6EW6
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
