In my Viking II used a 110/220VAC 20A solid-state relay (black square brick), which requires only 3 to 27VDC max to switch on the AC. The back of it is metal and acts as a heat sink and it only has 4 terminals. 2 terms (SPST) to switch on the hot side of the plate transformer’s primary, etc. and the other 2 terms are for the DC control. These relays can be found in most electronics catalogs and online stores. Mouser, Allied, Newark, etc.
Makes for a really simple PTT mod.
Just make sure that you have the SSR wired after the main power switch as a failsafe ! The failure mode of those bricks is shorted ON !.
They should never be used as a main power control without a normal backup in line.
Otherwise they work fine. I have installed several commercial sound systems using 40 amp rated SSR's for simple dumb operator single button or keyswitch power up. The racks had locked doors to prevent any unauthorized changes.
If buying these surplus make sure that they are of the zero crossing type, most common, as they are also available for use as phase control dimmers/speed controls and need an AC line sync'd square wave control voltage.
I use a small 2 amp block to power the 110V AC Dow Key when operating a transmitter other than the killer VKII's.
Once my shack is set up again will standardize the relay control voltages to something normal like 12-24 or so depending on what I have the most relays for.
Bill, KB3DKS in 1 Land