Ehrhorn Technological Operations ALPHA 76A, Руководство по эксплуатации и техническому обслуживанию, Страница: 6 / 19

re s u lt , along with grid current greatly in excess of normal.
4
I f drive power i s reduced below the tune-up level without further adjust­
ment o f TUNE and LOAD controls, am plifier e ffic ie n c y w ill be reduced.
Both o f these statements are applicable equally to any lin e a r am plifier
of the types used for high power amateur and sim ila r service.
I t i s therefore essential that the am plifier be adjusted for maximum r f
output at the drive and d-c input powers which are to be employed in
normal operation, WITH ONE IMPORTANT EXCEPTION: i f the plate voltage i s
changed without also changing the TUNE and LOAD adjustments, the re s u lt in g
power input level which w ill y ie ld optimum performance at the new plate
voltage w ill vary in proportion to the square o f the plate v o lta g e .
For
example, i f the ALPHA 76A is tuned up for maximum output with 1400 VDC
plate voltage (typical LV) and with the drive level set so that the
resultant maximum r f output i s about 700 watts (equivalent to a d-c input
of roughly 1000 watts), THEN when the plate voltage i s increased to 2000
VDC the am plifier w ill inherently perform optimally when driven to about
700 X (2000/1400)2 = 1400 watts r f output, corresponding to approximately
2000 watts d-c plate input.
In general, the final operating adjustment after basic tune-up should be
to set excitation (drive) from the exciter or transceiver so that the
GRID current meter indication j u s t reaches about 50 mAdc (1/3 scale) key-
down or on SSB voice peaks.
(b) INITIAL TUNE-UP - Place am plifier in STANDBY (both CW and SSB buttons out:
i f one is already depressed, p a r t i a l l y depress the other and release, so
that both pop out and show b la c k ) .
(1) Press HV button and watch MULTIMETER HV scale (0-3 KV).
(2) Press ON button and release. Panel meters should immediately illum i
nate amber or red and the MULTIMETER should swing promptly to i n d i ­
cate 1.5 KV
+_
100V (mid-scale). ( I f t h is does not occur, press OFF
immediately and locate the problem.) The blower should s t a rt immedi
ately and exhaust a i r should be detectable flowing from cover vents.
(3) When tube warm-up delay i s completed in approximately 60 seconds,
the meters w ill change to pale green or blue, in d icatin g "ready" to
transmit.
Set controls to the preliminary points indicated in
Table I below, depending on the desired operating frequency.
TABLE I — PRELIMINARY SETTINGS FOR INITIAL TUNE-UP
FREQ. MHZ BAND TUNE LOAD
f REQ.
BAND TUNE LOAD
1 .8 1 .8 84 30 7.1 7 50 45
2.0 1 .8 75 25 14.15 14
20
70
3.6 3.5 53 38 21.20 21 10 82
3.9 3.5 42 48
28.70*
28* 08* 9.0*
M£H
s u f f i x models only.
(4) Press CW button and switch the exciter to CW or TUNE; the ALPHA
panel meters should turn amber, indicating "transm it".
(5) VERY SLOWLY increase exciter c a r r ie r output until the am plifier
PLATE CURRENT meter indicates h a lf-sc a le - - about 0.5 ampere.