Photo 11 Power Relays
2 . 3 S m a l l S i g n a l Relay
Small signal relay is employed in preamplifiers for mut
ing, selecting equalizer's time constant, etc. Structure is
the same as that of protective relay. This can be made small
because it deals with a small current of low voltage.
Photo
1 3
Small Signal Relay
2 . 2 Protective Relay
Protective relay is for preventing damage to aparatus. This
deals with the signal of a wide dynamic range, from residu
al noise level ( l m V / O . l m A ) to the m a x i m u m output level
(28V/3.5A(100W output)) at 8 0 load. With this switch,
when the contact surfaces are oxidized or sulfurized, small
signal current will be blocked and sound will be muted by
the nonconductive oxide or sulfide film formed on the sur
face because it can not scrub the film off, or it can not
clean by itself. The film can be b r o k e n if the power out
p u t is high when the power is switched on a n d off. Such
a case, however, is unexpected because amplifier's volume
control is usually turned down when power is switched on.
Protective relay's contact points are m a d e of gilded silver
t o prevent the oxidization and sulfurization or doublepoint-
ed, or two circuits are used for one purpose to make the
contact perfect. In principle, the failure rate of the dual-
contact-point relay becomes 1
/X
2
if that of the single con
tact point relay is 1/x.
2 . 4 Reed Relay
Reed relay is m a d e of two flat magnetic strips of 52-gold
sealed in a tube filled with inert gas. Its contact points have
been gilded. When a current is applied to the coil, the leads
attract each other a n d close the circuit. When the current
stops, the circuit opens. The largest feature of this relay
is that contact points of this relay are not affected by the
environmental conditions because they are protected by an
inert gas. The use of this relay is the same as that of the
small signal relay.
Glass tube
Terminal
Fig. 11 Reed Relay
Photo 14 Reed Relay
Photo 12 Protective Relay
11
Au-plated
Terminal
52-gold (Ni 52%,
Fe 48%)
Coil
Inert gas
