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How to Key an SB220 Without a Foot Pedal

Heathkit's SB220 linear HF amplifier was designed and originally produced in an era when the typical HF transceiver utilized vacuum tubes and mechanical transmit-receive relays. Modern transceivers are all solid state, including a transistorized transmit-receive switch that often is not rated for the voltage and current that may be present in a vacuum-tube amplifier keying circuit. One solution to the problem is a foot switch that incorporates two separate contacts; one to key the transceiver and the other to simultaneously key the amplifier. There is another option that allows the transceiver to remotely key the amplifier via microphone PTT switch or VOX (voice-operated keying), without damage to the transceiver.

Things You'll Need

12-volt relay
RCA-to-RCA audio patch cable
Insulated hook-up wire
Utility knife
Soldering iron
Solder

Instructions

- 1
  Use the knife to cut the patch cord in the center. Strip and separate the two conductors on both patch cord segments.
- 2
  Solder the conductors of one patch segment to the two contact terminals of the relay. Solder the center conductor of the other patch segment to the negative control terminal of the relay.
- 3
  Strip 1/2-inch of insulation from each end of the hook-up wire. Solder one end of the hook-up wire to the positive control terminal of the station's 12-volt power supply.
- 4
  Plug the patch cord that is connected to the relay contacts into the "Ant Relay" jack on the rear panel of the SB220. Plug the control patch cord into the external relay jack on the transceiver. Now when you key the transceiver, the relay will automatically key the amplifier.

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