The [RELAY N.O.] output of the VI and VI+ must not see greater than 30 volts
DC from the circuit being keyed. The limiting factor appears to be the
voltage ratings of the RF bypass capacitor (C8) and the RC snubber network
capacitor (C14) which are placed across the relay (K1) contacts.
Ten Tec has a NOTE (in italics!) in the VI+ manual (Chapter 3, paragraph
3-6.16). The VI manuals did not have this caution noted.
If anyone is interested in a passive interface for amplifiers which exhibit
higher voltages on their PTT lines, such as the SB-220 (110 VDC), older
Collins amps, etc., I can email a schematic upon request. The circuit is a
"fail-safe" interface, which prevents greater than 15 volts from appearing
at the VI/VI+ [RELAY N.O.] output.
73, Dave, K1FK
Fort Kent, ME
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