Heathkit SB-101 back to start page
Heathkit once offered an optional frequency display for the HW and SB series of transceivers. This was the SB-650. It operated in the 3-30MHz range and calculated the receive/transmit QRG from the three internal oscillators. The frequency resolution was 100 Hz.
Today, it is difficult
to find a used, working SB-650 on hamradio markets. I
therefore decided to build my own SB-650 for my SB-101, which works
nicely. This is an up/down counter that considers the actual HFO-, BFO-
and VFO frequencies. All technical information about the SB-650 is
online available,
including the full schematic and circuit explanation. See for
example here: [Link].
I replaced the old TTL - ICs with the newer and smaller SMD versions
and the Nixie tubes by 7-segment LED displays. Two small PCB boards
were designed as well as a shielded enclosure, fitted on the left side
of the VFO. The LED display was placed behind the upper front window. Some adaptations of the original SB-650 circuitdesign
were necessary. The stabilized DC supply was derived from the heater
voltage. The project was a lot of work and a lot of fun. The
SB-650 ´successor´ works nicely. See the figures below.
Here is a look into the
shielded housing, made by copper-clad epoxy board. The boards are
single-sided. Cross-connections were made by enameled wire