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Inside the SB-104(A) Transceiver 

Written By: Ron Baker / WB4HFN

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This article on the Heathkit SB-104(A) Transceiver is a basic introduction to the radio.   This transceiver was the first all solid state transceiver produced by Heathkit in the early 1970's.   Some would say it was the first  American made all solid state transceiver.  The Heathkit designer of the SB-104 was Mike Elliot, who a couple of years later went to work for the RL Drake company and designed the Drake TR7 transceiver.   After a couple of years in design the SB-104 was introduced for Christmas 1974.    Three years later the improved SB-104A was introduced in the fall of 1977 and sold in kit form for $669.95.   Even though this radio came with a few problems and peculiarities overall it was a great performing and easy to use radio.    One of the many features that set this radio apart from all the other transceivers available was the band switching and the all solid state no-tune power amplifier.   With this radio design gone with the days of tuned circuits wired around a large ganged rotor switch.   Heathkit put the tuning circuits on the circuit boards and used diode switching to change the bands.    The "Band Switch" was just a single wafer that switched a voltage to the individual boards having band selectable circuits.   On the individual circuit board Heathkit used this voltage to forward bias pin diode switching circuits to select the appropriate operating band.

Another unique innovation in this radio was the all solid state broadbanded RF power amplifier with a flat frequency response from 3 to 30Mhz.  What this means to the operator, no more transmitter tuning with band changes.

Shown below are pictures of the front, rear and side views of the transceiver.  The last picture is the inside on the radio where you can see where each circuit board is placed.   The next few pages show up close pictures of each of the circuit boards in the radio with a brief description of the board and its functions.   The last page in the article talks about hooking the transceiver to a power source, connecting up the accessories, a few of the more common problems with the radio and some quick fixes and troubleshooting tips.

Pictured here is the front view of the transceiver, note the simple layout of the controls and switches.  This radio was one of the first transceivers to have a frequency digital readout.

The rear panel layout and connector labeling of the SB-104(A) Transceiver made simple interconnecting other station equipment and power supply.   Note the jumper between the VFO "Input" and "Output", this coax jumper must be in place for the transceiver to operate when not using the SB-644 Remote VFO.     The antenna connector, centered under the heat sink, will accommodated an external receiver.    Make sure the switch adjacent to the antenna connector is set to the "Common" position unless an external receiver is being used.  The external receiver antenna connector is marked "REC", on the far left.

This side view of the radio really gives you the idea of its size, it wasn't a small radio, but it was fairly light weight as compared to other transceiver introduced during this period.   Access to the inside and all the circuit boards was quick, just looses the two screws on either side and lift the top half of the case off.

This picture shows the inside layout of the transceiver and the placement of each circuit board in the radio.  Because of its size every board is easily accessible and has plenty of room to work.   The radio came with a circuit board extender which made easy work to troubleshoot and align the individual circuit boards.

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