[Amps] Vac relay coils in series ?

[jim.thom jim.thom@telus.net]

I'm installing  3x vac relay's into an amplifier.  (Input, output, and cut
off bias).  Coils are available for both 12 vdc ( 80 ohms)....and also 26.5
vdc  ( 335 ohms).  The amp has to be able to handle a kw on bypass, since I
series 2 or more amps...tuned up on each end of the same band, or tuned up
on different bands.   A simple rotary switch is used to engage only one key
line at a time.  Simple interlock.  IE: switch positions  1+3+5+7 are used
for amplifiers  A-B-C-D.   Switch positions 2+4+6+8  are used for bypass.

What is the 'normal'  failure mode for a vac relay ?   Is it the  coil that
goes open, or does the armature inside  bind up, and then stuck ?

The thought here is, IF the coils are wired in series, say 3 x 12 vdc
coils...and if any one coil ever opened up...then none of the relay's
would operate.

Worse case scenario is if the OUTPUT relay failed to operate..... then
drive is still applied...and NO  ant  connected  to the output of the amp.

But I don't know what the ..'normal' failure mode of a vac relay is.   I'm
talking about the HC-1,  RJ1A,  GH-1  type relays.  They all have a screw
on the base, to swap coils.  IE: coils are field replaceable..with either a
12 vdc or  26.5 vdc coil.

I use a delay in the TX inhibit lead on the xcvr, (to give the relays in
the amp a head start) so the exact sequencing of the 3 x relays is a moot
point.

I have a choice of either 31 vdc or  62 vdc to power the 3 x relays.   IE:
31 vdc + a  19 ohm  series drop  resistor to  power  3 x 26.5 vdc coils in
parallel.

 OR   use  62 vdc + a 173 ohm series  drop resistor, to power  3 x 12 vdc
coils in series.

Tnx.... Jim   VE7RF