> The FL2100 'RY' relay control switches 12V @ 200mA only.
Use a voltmeter to check the keying line on your FL-2100
or FL-2100B. The manuals for both of those amplifiers show
a relay keying voltage between -13V and -18V. The relay
voltage is derived from a 13V transformer winding through
a half-wave rectifier (series diode) and 1000 uF capacitor.
the -16V (+/-) under load is used for both grid bias and
Note, if the amplifier was ever modified to use Svetlana 572B
tubes, the half-wave rectifier may have been replaced by a
voltage doubler and the open circuit relay voltage would be
In either case, the FL-2100/2100B will not work directly with
the K3 "Key Out" signal.