Ehrhorn Technological Operations ALPHA 76A, Operating And Technical Manual, Page: 8 / 19

Operating Notes:
(a) TUBES - The 8874 ceramic triodes are extremely rugged and normally operate
with a large margin of safety. They w ill d e live r outstanding service l i f e
IF not damaged by g r o s s ly excessive grid d iss ip a tio n or a irflo w blockage
(keep the intake and exhaust vent areas c le a r!)
DO NOT ALLOW AVERAGE PLATE
CURRENT PER TUBE TO EXCEED 0.35 AMPERE FOR MORE THAN 5-10 SECONDS, NOR EVER
TO EXCEED 0.5 AMPERE.
DO NOT ALLOW GRID CURRENT TO EVER EXCEED FULL SCALE
(150 mA); normal operation requires only 50-60 mA for two tubes or 75-90 mA
for three.
(b) INTERLOCKS - The ALPHA 76A se rie s i s equipped with switches which shut o ff
a-c power and short out the high voltage power supply when the cover is
not securely fastened in place.
THESE PROTECTIVE INTERLOCKS ARE PROVIDED
TO PROTECT YOU AGAINST POTENTIALLY FATAL ELECTRIC SHOCK RESULTING FROM
CONTACT WITH LETHAL OPERATING VOLTAGES INSIDE THE AMPLIFIER.
THE AMPLIFIER
SHOULD NEVER BE ENERGIZED WITH THE COVER REMOVED AND INTERLOCKS DEFEATED
EXCEPT BY THOROUGHLY TRAINED AND KNOWLEDGABLE SERVICE PERSONNEL!
(c) FUSES - Except in rare instances o f component f a ilu r e , the blowing of one
or both primary lin e fuses indicates that the maximum safe average power
input c a p a b ility o f the am plifier has been s u b s t a n t ia lly exceeded. USE
ONLY 10A CERAMIC FUSES, EXCEPT 15A for 76CA option, up to 20A for 120V
operation.
(Standard g la ss fuses of the same size are rated for c i r c u i t s
up to 32 V only, and may shatter or explode within the fuse holder.)
The slo -b lo fuse F3 located j u s t behind the front panel prevents burn-out
of the ste p -sta rt r e s is t o r s and HV r e c t i f i e r s in the event of abnormal
turn-on conditions or HV fa u lts.
DO NOT SUBSTITUTE a fuse of different
type or rating.
(d) PLATE OVERCURRENT RELAY - This relay functions prim arily to de-energize
the primary power c i r c u i t quickly in the event of a fa u lt in the HV c i r ­
c u itry or g r o s s ly excessive drive conditions.
The relay should not be
re lie d on to prevent damage from either short- or long-term overdrive;
that i s the op e rator's r e s p o n s ib ilit y .
Should the overcurrent relay t r ip ,
removing a ll a-c power from the am plifier, i t i s essential to determine
and correct the cause before re-applying power by pushing the ON button.
(e) MAINTENANCE AND TROUBLESHOOTING - Most apparent f a ilu r e s and problems with
ALPHA am plifiers r e s u lt from operators' f a ilu r e to read and thoroughly
understand the contents o f t h is manual, as well as basic lin e a r amplifier
p rin c ip le s - - rather than from actual equipment defects.
The am plifier in t e r io r , p a r t ic u la r ly the high voltage d-c areas of the
power supply and r f compartment, should be cleaned frequently enough (with
a soft brush and vacuum cleaner) to prevent v i s i b l e accumulation o f dust.
I f extremely dusty conditions p re vail, i t may be advisable to secure a thin
p la s t ic a i r f i l t e r , of the type used in window a i r conditioners, across the
a ir-in t a k e area.